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Test answers for Material Engineering 2016

(89) Last updated: January 27
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89 Answered Test Questions:

1. True or False: Interstitial diffusion occurs more rapidly than vacancy diffusion.

Answers:

• False

• True

2. Given a material with yield strength 310 MPa and a factor of saftey 5, what is the working stress

Answers:

• 305 MPa

• 315 MPa

• 1550 MPa

• 62 MPa

3. How can the diffusion velocity be quantified?

Answers:

• Einstein's law

• Hooke's law

• Newton's law

• Fick's law

4. On tensile test,does the plane of rupture says anything about the mechanical nature of the materials?

Answers:

• Yes, if the material has high or low hardness

• No, there isn’t any relation between the plane of rupture and the nature of the material

• Yes, if the material is brittle or ductile

5. Does the geometry have an influence on the critical failure modes that may occur on a material upon mechanical loading?

Answers:

• Yes

• No

• No, the failure modes depend only on the material

6. The eutectic alloy is the alloy with lowest melting point on an eutectic system. True or false?

Answers:

• False

• True

7. A rod of initial length 10 cm is placed under load. The rod's new length is measured at 10.5 cm. What is the engineering strain of the material under this load?

Answers:

• 0.048

• 0.05

• 0.952

8. Which mechanical properties can be determined from tensile test?

Answers:

• Density, Yield strength, Melting point

• Young’s Modulus, Density , Melting point

• Young’s Modulus, Yield strength, Rupture strength

9. On the martensitic transformation, the ratio between the height of the tetragonal structure in relation to the other dimensions, which are equal, depend on the carbon content. True or False?

Answers:

• True

• False

10. How is materials selection  usually performed?

Answers:

• Encyclopedia

• Atlas

• Handbooks

• Materials selection charts

11. What are the main characteristics of metals?

Answers:

• High Young’s Modulus, high density, low toughness

• Low Young’s Modulus, low density, low toughness

• High Young’s Modulus, high density, high toughness

• High Young’s Modulus, low density, low toughness

12. Which one of these can be considered as defects if they exist on a material

Answers:

• Gaps and dislocations

• Gaps but not dislocations

• Dislocations but not gaps

13. How would you determine the material properties obtained from a tensile test?

Answers:

• By means of a load-strain chart

• By means of a stress-strain chart

• By means of a stress-load chart

14. What is the stable form of pure iron at room temperature?

Answers:

• pearlite

• austenite

• cementite

• ferrite

15. When a metal is cooled, what happens at a microstructural level?

Answers:

• Formation of Nuclei and then the growth of nuclei originating crystals

• Formation of Nuclei and then the growth of nuclei but not originating crystals

• No important changes occur at the microstructural level

16. Is the material cost always the most important factor for materials selection?

Answers:

• No, not always

• Yes, always

17. The aim of steel quenching is to give to the material

Answers:

• The maximum hardness

• The maximum stiffness

• The lowest ductility

18. How are the [100] direction and the (100) plane oriented with respect to each other?

Answers:

• parallel

• perpendicular

• no correlation

19. An identical amount of liquid metal is poured into two moulds, one with smooth walls and one with rough walls, which are then cooled. Which batch will begin solidification at a higher temperature?

Answers:

• The batch in the smooth-walled mould

• The two batches will begin solidifaction simultaneously.

• The batch in the rough-walled mould

20. True or False: appreciable solid solubility requires that the solvent and the solute share a crystal structure.

Answers:

• True

• False

21. Which of the following is NOT a characteristic of aluminum and aluminum alloys?

Answers:

• high melting temperature

• high corrosion resistance

• high electrical conductivity

• high thermal conductivity

22. Why do materials get oxidated?

Answers:

• Because the reactions originating the oxidated compound increase the energy of the system, and, therefore, the system becomes more stable

• Because the reactions originating the oxidated compounds lower the energy of the system, and, this tendency depends strongly of the material

• Because the reactions originating the oxidated compound lower the energy of the system, and, this tendency is equal for every material

23. Which of the following is a typical application of low-carbon steel?

Answers:

• knives

• chemical storage tanks

• gears

• structural steel componenets

24. Is it possible to determine Poisson coefficient experimentally?

Answers:

• No, It is not possible

• Yes, by doing a tensile test on the elastic domain

• No, It is not possible, but can be calculated if the longitudinal elasticity modulus and the transversal elasticity modulus are known

25. Which of the following factors does not influence diffusion?

Answers:

• The electrical conductivity of the material

• The crystal structure of the matrix material

• The atomic radius of the diffusing species

• The temperature

26. What is the maximum carbon content of steels?

Answers:

• 2%

• 1%

• 1,50%

• 2,50%

27. A copper wire or radius 3 mm is to offer no more than 10 ohms resistance. What is the maximum length of the wire, given σ = 6.0×10^7 (Ω•m)^-1 for copper?

Answers:

• 17 m

• 570 m

• 1.7 m

28. Given a <2% contentration of carbon (atomic radius 0.071 nm) in iron (atomic radius (0.124 nm), will the solid solution formed be substitutional or interstitial, or will second phase form instead?

Answers:

• interstitial

• a second phase will form

• substitutional

29. In non-equilibrium cooling of a binary system, what happens to the distribution of the two elements in the final grains?

Answers:

• There will be a concentration gradient, with the center of the grain rich in the lower-melting element and the grain boundaries rich in the higher-melting element.

• There will be a concentration gradient, with the center of the grain rich in the higher-melting element and the grain boundaries rich in the lower-melting element.

• The elemental composition of the grains will be uniform

30. In steady-state diffusion, increasing the area across which the diffusion occurs will have what effect on the concentration profile?

Answers:

• The concentration profile will have a steeper slope

• The concentration profile will be uneffected.

• The concentration profile wil have ashallower slope

31. What are the main characteristics of polymers?

Answers:

• Low Young’s Modulus, low density, low strength

• Low Young’s Modulus, high density, low strength

• High Young’s Modulus, low density, low strength

• High Young’s Modulus, high density, high strength

32. When Luders bands occur

Answers:

• They can be effectively treated with a procedure which eliminates free dislocations

• They cannot be effectively treated

• They can be effectively treated with a procedure which creates free dislocations

33. In general, at any given temperature which of the following diffusions paths is fastest?

Answers:

• Diffusion along surfaces

• Diffusion along grain boundaries

• Diffusion through a defect-free crystal lattice

34. True or False: Hardness is an absolute material property.

Answers:

• False

• True

35. What is the relationship between the rate of solidification and the time required for solidification to proceed to some degree of completion (e.g. time to 50% solidification comlpetion)?

Answers:

• They are directly proportional.

• They are inversely proportional.

• They are uncorrelated.

36. On crystalline solids, the dislocations :

Answers:

• May be formed by plastic deformation, but not by solidification

• May be formed during solidification, but also by plastic deformation

• May be formed during solidification, but not by plastic deformation

37. In order to form a substitutional solid solution what must be true of the relationship between the atomic radii of the solute and solvent atoms?

Answers:

• The atomic radius of the solute atoms must be much smaller then that of the solvent atoms

• The atomic radii of the solute and solvent atoms must be close to each other

• The atomic radius of the solute atoms must be much larger then that of the solvent atoms

38. Consider two materials, with the exact same properties except the yield strength, which is higher in one of them. The material with higher yield strength:

Answers:

• Yields at a higher load intensity

• Has higher Young's Modulus

• Is better in terms of stiffness

39. During heat treatment, shape distortions can occur. What is a possible solution to minimize shape distortions that occur during austenitization?

Answers:

• Decrease the maximum temperature and increase the phase time during the constant temperature phase

• Increase the maximum temperature and decrease the phase time during the constant temperature phase

• Decrease the maximum temperature and phase time during the constant temperature phase

40. Which of the following iron-carbon phase is formed by a diffusionless transformation?

Answers:

• spheroidite

• pearlite

• martensite

• bainite

41. Two samples of a ceramic are formed from a powdered precusor material. Subsequent to compaction and forming, sample A has 0.2 volume fraction porosity, while sample B has 0.4 volume fraction porosity. Which sample has a higher modulus of elasticity?

Answers:

• Both A and B have the same modulus of elasticity.

• A

• B

42. For structural applications, what shall be the offset for the determination of the yield stress?

Answers:

• 0,15%

• 0,10%

• 0,25%

• 0,20%

43. Which will have a higher surgface free energy: a solid nucleus surrounded by liquid phase or a nucleus on a solid surface?

Answers:

• a nucleus on a solid surface

• a nucleus in the liquid

44. If electroneutrality is to be preserved, which of the following point defects is not possible in NaCl when a Ca2+ ion substitutes for an Na+ ion?

Answers:

• one Cl- interstitial

• one Na+ vacancy

• one Cl- substitutional

45. In graphite, the carbon atoms are arainged in sheets. What type of bond exists between the atoms in a sheet and what type between sheets?

Answers:

• ionic, covalent

• van der Waals, ionic

• covalent, van der Waals

• ionic, van der Waals

46. When a material is plastically deformed:

Answers:

• If the load is removed, all the deformation is lost

• The Hooke's law is valid to predict the mechanical behavior if the load is tensile

• The material has not suffered yield

• The dislocations move

47. Plastic deformation in metals is accomplished by what process?

Answers:

• strain hardening

• twinning

• crack formation

• slip

48. An increase in temperature will have what effect on the diffusion coefficient of a material

Answers:

• The diffusion coefficient will decrease exponentially.

• The diffusion coefficient will decrease linearly.

• The diffusion coefficient will increase linearly

• The diffusion coefficient will increase exponenetially

49. On a steel, what is the effect of increasing the carbon content?

Answers:

• The ductility decreases, but the elongation increases

• The ductility and the elongation increase

• The ductility increases but the elongation decreases

• The ductility decreases, so as the elongation

50. Which of the following is not a bulk property of a material?

Answers:

• modulus of elasticity

• electrical conductivity

• thermal conductivity

• resistance

51. What happens when excess solute is added so a solution above the solution's solubility limit?

Answers:

• The solution heats up, raising the solubility limit.

• The additional solute forms a new phase.

• The additional solute can not be added to the solution.

• The solution becomes supersaturated.

52. What happens over time to the microscruture of an alloy of two elements A and Bquenched into a spinodal region of its phase diagram?

Answers:

• The initial uniform phase segregates over time into A-rich and B-rich regions.

• Initial separate A-rich and B-rich regions merge suddenly into regions of uniform phase.

• Initial separate A-rich and B-rich regions merge over time into regions of uniform phase.

• The initial uniform phase suddenly segragates into A-rich and B-rich regions.

53. For tools made of steel, if the part suffers fracture, the carbon content shall:

Answers:

• Be increased

• Be decreased

• Be kept constant, but alloying elements shall be decreased

• Be kept constant, but alloying elements shall be increased

54. What is the driving force for solidification?

Answers:

• A negative change in Gibb's free energy

• A positive change in Gibb's free energy

• Cooling below the equilibrium melting temperature

55. After steel quenching, a tempering is usually performed. The aim of the tempering is:

Answers:

• To further decrease the ductility

• To increase the toughness

• To further increase the hardness

• To further increase the stiffness

56. The Luders bands:

Answers:

• Are a characteristic of the metals with any carbon content, but that crystallize with face centered cubic (FCC) structure

• Are a characteristic of the steels with high carbon content (>1% wt)

• Are a characteristic of the steels with low carbon content (<0,2% wt)

57. When ceramics are sintered:

Answers:

• The structural strength increases and density is kept constant

• The structural strength increases and density decreases

• The structural strength increases and there is an increase in the porosity

• Both structural strength and density increase

58. In a binary isomorphous system the liquidus line seperates what two phases?

Answers:

• The liquid phase and a phase consisting of a mixture of liquid and solid.

• The liquid phase and the solid phase

• The solid phase and a phase consisting of a mixture of liquid and solid.

59. When nickel is added as an alloying element to steel what is the effect?

Answers:

• Decreased eutectoid temperature and increased eutectoid composition (wt% C).

• Increased eutectoid temperature and decreased eutectoid composition (wt% C).

• Increased eutectoid temperature and eutectoid composition (wt% C).

• Decreased eutectoid temperature and eutectoid composition (wt% C).

60. What are auxetic geometries?

Answers:

• Are geometries that get thinner in the transversal direction while loaded in tension in the longitudinal direction

• Are geometries that stretch in the transversal direction and longitudinal direction equally while loaded in tension in the longitudinal direction

• Are geometries that stretch in the transversal direction while loaded in tension in the longitudinal direction

61. What is the Elasticity Modulus and what does it represent?

Answers:

• It represents the stiffness of the materials, and it is always valid, regardless of the considered domain

• It represents the stiffness of the materials, and the higher the value, the more elastic and less rigid is the material

• It represents the stiffness of the material, without accounting the geometry, on the elastic domain only

62. which one of these is the material with the highest Elasticity Modulus: Low-alloy steel, Stainless steel,Titanium,Tungsten or Copper

Answers:

• Tungsten

• Titanium

• Stainless steel

• Low-alloy steel

63. In general, which of the following orderings best describes the typical values for linear coefficient of thermal expansion for different classes of materials?

Answers:

• polymers > metals > ceramics

• metals > polymers > ceramics

• metals > ceramics > polymers

• ceramics > metals > polymers

64. What is The crystallographic structure of Gamma, Delta and Alpha irons?

Answers:

• Delta and Alpha are face centered cubic and Gamma is body centered cubic

• Delta and Gamma are face centered cubic and Alpha is body centered cubic

• Delta and Alpha are body centered cubic and Gamma is face centered cubic

• All are body centered cubic

65. In a typical engineering strees-strain curve, the tensile strength of the material under test is the stress measured at what point?

Answers:

• The point where the curve departs from linearity.

• The point of fracture.

• The maximum point of the curve.

66. Imagine that for a part subjected to mechanical loads, the aim is to have the lightest material but with the best mechanical behavior in terms of deflections. Which approach is the most effective?

Answers:

• Materials selection with the aim of increasing Yield strength

• Design improvements with the aim of maximizing Inertia moment

• Both are equally effective

67. The steels which will be plastically deformed and used to produce sheet have carbon content:

Answers:

• Lower than 0,1%

• higher than 0,55%

• Between 0,25-0,55%

• Between 0,12-0,25%

68. Grain boundaries are defects. True or False?

Answers:

• False

• True

69. What kind of composite best describes concrete?

Answers:

• Laminated composite

• Large-particle composite

• Fiber-reinforeced composite

• Dispersion-strengthened composite

70. As a solid nucleus grows, where are atoms arriving from the liquid phase most likely to attach?

Answers:

• At an atomic ledge

• On a flat atomic surface

• At a grain boundary

71. In a sample under tensile stress the maximum stress corresponds to what phenomenon in the sample?

Answers:

• The transition from elastic to plastic deformation.

• No predictable phenomenon.

• The onset of necking in the deformed sample.

• The fracture of the sample

72. Vulcanization of rubber is an example of changing a thermoset to a thermoplastic via what mechanism?

Answers:

• plasticizing

• crosslinking

• condensation polymerization

• adition polymerization

73. What effect is to be expected on the thermal conductivity of a material with a unit cell having a high degree of vibrational freedom?

Answers:

• The material will have low thermal conductivity.

• The material will have high thermal conductivity.

• Vibrational modes have no effect on thermal conductivity.

74. On an eutectic reaction, when the material is cooled:

Answers:

• 1 liquid phase originates 2 solid phases

• 1 liquid phase originates 1 solid phase

• 2 liquid phases originate 1 solid phases

• 2 liquid phases originate 2 solid phases

75. The purpose of annealing worked steel is to convert the pearlite grains that are the result of plastic deformation into what phase and microsctructure?

Answers:

• Fine-grained autenite.

• Fine-grained ferrite

• Coarse-grained austenite

• Coarse-grained ferrite

76. When a material is heated above its Curie temperature what happens to its saturation magnetization?

Answers:

• The staturation magnetization falls to an equilibrium value

• The saturation magnetization rises to an equilibrium value.

• The saturation magnetization drops abrubtly to 0.

• The saturation magnetization drops gradually to 0.

77. For structural applications including mobile parts, what pair of properties would you consider to be most relevant for materials selection?

Answers:

• Rupture strength, density

• Young’s Modulus, density

• Young’s Modulus, rupture strength

78. The temperature of an extrinsic semiconductor is raised within its extrinsic region. What is the effect on carrier concentration?

Answers:

• Carrier concentration increases.

• Carrier concentration decreases.

• There is no effect on carrier concentration.

79. How does work hardening alter the stress-strain curve of a material under tensile load?

Answers:

• The slope of the stress-strain curve increases as the material undergoes work hardening

• Work hardening has no effect on the stress-strain curve of a material.

• The slope of the stress-strain curve decreases as the material undergoes work hardening

80. In a cubic crystal with side length 1 what is the coordinate of the of end point of a vector in the [120] direction?

Answers:

• (1/2, 1, 0)

• (1, 2, 0)

• (1, 1/2, 0)

• (1, 1/2, 0)

81. For tools made of steel that will be working at high temperatures, shall be selected a steel that:

Answers:

• May suffer primary hardening

• Contain Manganese (Mn) and Nickel (Ni)

• May suffer secondary hardening

82. Equilibrium cooling of an alloy of eutectic composition results in what final composition?

Answers:

• one solid phase and one liquid phase with compositions corresponding to the end of the eutectic isotherm and the eutectic point, respectively

• two solid phases with compositions corresponding to the ends of the eutectic isotherm

• one solid phase with composition corresponding to the eutectic composition

• one liquid phase ithe eutectic composition

83. An iron-carbon alloy of eutectoid composition (0.76 wt% C) is cooled from a temperature in the γ phase region into the α + Fe3C region. What is the resultant microstructure?

Answers:

• Thin alernating layers of α and Fe3C.

• Grains of graded composition from Fe3C-rich center to α-rich boundary

• Grains of graded composition from α-rich center to Fe3C-rich boundary

• Intersecting cross-hatched layers of α and Fe3C.

84. The coordination number for the face-centered cubic (FCC) crystal structure is:

Answers:

• 12

• 8

• 4

• 6

85. Of these, which material would you expect the highest extension on rupture obtained on a tensile test: Magnesium, Steel-nickel, Stainless steel, Structural steel, Aluminum

Answers:

• Magnesium

• Steel-nickel

• Stainless steel

• Structural steel

86. The diffusion of matter:

Answers:

• Occurs to minimize the free energy of the system and is a process of chemical composition homogenization

• Occurs to minimize the free energy of the system

• Is a process of chemical composition homogenization

87. The solid solubility of silicon in aluminum is 1.25 atomic % at 550¡C (823K) and 0.46 atomic % at 450¡C (723K). What solubility would be expected at 200¡C? (R=8.314)

Answers:

• 0.006 atomic %

• 0.0324 atomic %

• 1.7 atomic %

• 6.370 atomic %

88. Copper has an FCC crystal structure. Given an atomic radius of 0.128 nm and and atomicweight of 63.54 g/mol, what is copper's theroretical density in g/cm^3?

Answers:

• 8.14 g/cm^3

• 8.89 g/cm^3

• 8.96 g/cm^3

89. An increase in a material's yield strength will have what effect on its plane strain fracture toughness KIc?

Answers:

• KIc will increase.

• KIc will decrease.

• Increasing the yield strength of a material will have no effect on KIc.