SE 2 Structural Materials Midterm Exam

For each problem, choose one and only one most relevant answer on a Scantron sheet.

1. Which one of the following is NOT a materials family: (A) Glasses (B) Ceramics (C) Aluminum alloys (D) Composite/hybrid materials

2. Which of the following is NOT regarded as a hybrid (composite) material?

(A) Straw-Brick (B) Carbon fiber reinforced polymer (CFRP) (C) Glass fiber reinforced polymer (GFRP) (D) Alumina (Al2O3)

3. Which one of the following is NOT a major characteristic of most polymers: (A) High stiffness (B) High ductility (C) Low mass density (D) Thermal sensitivity

4. You are choosing to buy custom paper clips. In order to hold as many pieces of paper as

possible without permanently deforming the paper clip, you want the paper clip made from the material with the highest (A) Ultimate tensile strength

(B) Yield strength (C) Stiffness (D) Fracture toughness

5. Sand casting and injecting molding are __________.

(A) Primary shaping methods (B) Secondary shaping methods (C) Joining methods (D) Deformation methods

6. Regarding metals and alloys, which of the following is true?

(A) Their toughness is low (B) They lack strength (C) They are electrically nonconductive (D) They are stiff

Avogadro's number = 6.02×1023 1 lbf = 4.45 N 1 nm = 10 Å = 10-3 micron (μm) = 10-9 m

7. You are trying to buy a pan which would not warp upon heating to high temperatures. It

would be best to look at the (A) Coefficient of thermal expansion

(B) Diffusivity of the pan (C) Maximum service temperature

(D) Yield strength at high temperatures 8. A bridge must be sufficiently strong to support at least a 10-ton load. This is

(A) An objective (B) A constraint (C) A free variable (D) None of the above

9. Which of the following is an example of a secondary process?

(A) Casting an iron ingot (B) Drilling a hole in a steel plate (C) Polishing the surface of a gear (D) Forging a steel plate into an auto frame

10. In a regular materials selection process, constraints can be used to (A) rank short-listed candidates (B) create free variables (C) reduce functional requirements (D) determine which materials are irrelevant

11. In a modulus-density bubble chart (the horizontal axis is density and the vertical axis is

Young’s modulus), material “A” is at the upper-right corner and material “B” is at the lower-right corner. Thus, it can be concluded that (A) Material “A” is less stiff than “B” (B) Material “A” is stiffer than “B” (C) Material “A” is more lightweight than “B” (D) Material “A” is heavier than “B”

12. By using a spring scale, it is measured that under ambient condition the weight of a piece

of unknown material is 10.00 lbs; if the measurement takes place in a vacuum chamber, the result becomes 10.02 lbs. What is the mass density of this material? (Hint: the density of air is 1.2 kg/m3). (A) 0.3 g/cm3 (B) 0.6 g/cm3

(C) 0.9 g/cm3 (D) 1.2 g/cm3

13. There are ____ different basic modes of loading.

(A) 2 (B) 3

(C) 4 (D) 5

14. The figure on the right shows

(A) torsion stress (B) compression stress (C) friction stress (D) shear stress

15. A piece of metal is placed under water 300 m deep. Its density increases by 0.05%. What

is the bulk modulus of this metal? (Hint: the hydrostatic pressure under water increases by ~1 atmosphere pressure, close to 0.1 MPa, per 10 m depth). (A) 60 GPa (B) 30 GPa (C) 300 GPa (D) 300 MPa

16. In the above problem, the Young’s modulus of this metal is likely to be

(A) 60 GPa (B) 30 GPa (C) 300 GPa (D) 300 MPa

17. The figure on the right shows the tensile

curves of four different titanium (Ti) alloys. According to the figure, the Young’s modulus of the Ti-8Nb-13Zr alloy is most close to which one of the following? (A) 500 GPa (B) 50 GPa (C) 50 MPa (D) 500 MPa

18. In the above problem, the yield strength of

the Ti-18Nb-13Zr alloy is most close to which one of the following? (A) 680 MPa (B) 550 MPa (C) 410 MPa (D) 280 MPa

19. In a tensile test, true stress is always larger than engineering stress. This is

(A) true (B) false

20. A copper rod is subjected to a tensile stress. Before loading, the initial length is 1 foot,

and the initial diameter is 1 in. After loading, the length becomes 1 foot and 1/4 in. What

is the true strain? (A) 2.08% (B) 2.06% (C) 25% (D) 1.25%

21. The Poisson’s ratio of copper is about 0.3. In the above problem, after loading, the

diameter of the rod should (A) decrease by about 0.006 in (B) increase by about 0.006 in (C) increase by about 0.08 in (D) decrease by about 0.004 in

22. Among the following atomic structures, _____ structure has the lowest packing fraction.

(A) FCC (B) BCC (C) HCP (D) amorphous

23. The net number of atoms in a BCC unit cell is ______________

(A) 2 (B) 4 (C) 9 (D) 15

24. Tungsten (W) has an atomic mass of 183.84 and an atomic radius of 0.14 nm. Its

crystalline structure is BCC. What one of the following is most close to its mass density? (A) 10 g/cc (B) 19 g/cc (C) 38 g/cc (D) 85 g/cc

25. Compared with the answer of the above problem, if the crystalline structure of Tungsten

were FCC, its mass density should (A) increase (B) decrease (C) remain the same (D) no sufficient information

26. A composite material is fabricated by reinforcing epoxy resin with 35 vol% glass fibers.

The Young’s moduli of epoxy and glass fiber are 10 GPa and 500 GPa, respectively. The mass densities of epoxy and glass fiber are 1.5 g/cc and 4 g/cc, respectively. What is mass density of the composite? (A) 1.2 g/cc (B) 2.0 g/cc

(C) 2.4 g/cc (D) 5.5 g/cc

27. In the above problem, which one of the following is likely the stiffness of the composite?

(A) 450 GPa (B) 250 GPa (C) 150 GPa (D) 15 GPa

28. We are choosing material for a helical spring. The spring must fit into a spring box; that

is, its total length and diameter should not exceed given limits. The diameter of the wire should fit with the holding hole in the spring box. Which one of the following would lead to the highest spring stiffness (spring constant)? (A) Titanium (Ti) alloys (B) Polypropylene (PP) (C) Lead alloys (D) Teflon (PTFE)

29. We are designing a flexible fixture, which can be regarded as

a cantilever beam with one end fixed in a wall-mounting system and the other end free, as shown by the figure on the right. It supports a concentrated transverse load that is applied at the free end. Its mass should not exceed a given value, M. Its cross section must be square and exactly fit with the square hole in the wall-mounting system. As a load is applied, the fixture should have a deflection as large as possible. What is NOT a free variable: (A) Choice of material (B) Cost of the fixture (C) Length of the fixture (D) Stiffness of the fixture

30. In the above problem, what is the objective?

(A) Choice of material (B) Mass of the fixture (C) Width of the fixture (D) Stiffness of the fixture

31. In the above problem, to choose the best material, which performance index should we

use? (E = Young’s modulus; ρ = mass density; b = cross-sectional size) (A) E/ρ (B) E1/2/ρ (C) Eρ3 (D) b10/M3

32. In the above problem, among the following materials, which one is the best choice?

(A) Polymer foams

(B) Tungsten (W) alloys (C) Boron carbide (B4C) (D) Polyurethane

33. Past the yielding point, materials undergo plastic deformation. This condition is volume

conservative; i.e., a material does not change its volume while under plastic deformation. Therefore, (A) Poisson's ratio is less for plastic deformation than it is for elastic deformation

(B) Poisson's ratio is close to 0.5 during plastic deformation. (C) The bulk modulus is nearly 0.3 during plastic deformation. (D) Young's modulus changes to zero during plastic deformation.

34. We are choosing a material to build a lightweight, stiff structure. The performance index is M = E1/3/ρ. The structure made of a material with index M = 5 can be how many times lighter than one with M = 1? (A) 5 times

(B) 1.71 times (C) 50 times (D) 125 times

35. The yield strength of a copper alloy is 50 MPa. A 20-gram diamond is placed on it, with a pyramid-shaped tip against the copper surface. The diamond will (A) be damaged (B) leave a dent of about 63.2 microns in copper (C) leave a dent of about 36.5 microns in copper (D) not damage the copper at all

36. A high-carbon steel is harder than a low-carbon steel; that is,

(A) A high-carbon steel has a higher Young’s modulus (B) A high-carbon steel has a lower stiffness (C) A high-carbon steel is more ductile, i.e. has a higher toughness (D) A high-carbon steel has a higher yield strength

37. A high-carbon steel is harder than a low-carbon steel, which is likely caused by

(A) the strong atomic bonds in the high-carbon steel (B) the high dislocation density in the high-carbon steel (C) the high resistance to dislocation motion in the high-carbon steel (D) the high purity of the high-carbon steel

38. Plastic deformation in a metal is NOT related to

(A) the nonlinear section of stress-strain curve (B) the formation of vacancy defects (C) the behavior of dislocations (D) the breakage of atomic bonds

39. The figure on the right depicts a (A) screw dislocation (B) edge dislocation (C) grain boundary (D) perfect crystal

40. Which one of the following is NOT true?

(A) The motion of a screw dislocation is directly driven by a shear stress (B) The motion of an edge dislocation is directly driven by a shear stress (C) The motion of an edge dislocation is directly driven by a tensile stress (D) Screw and edge dislocations can move simultaneously

41. The figure on the right depicts a unit cell in a copper crystal.

A tensile stress of 50 MPa is applied along direction FA. What is the resolved shear stress along slip direction BD in slip plane DEBG? (A) 0 (B) 12.6 MPa (C) 37.8 MPa (D) 20.4 MPa

42. In the above problem, if the tensile stress of 50 MPa is applied along BH, the resolved

shear stress along slip direction BD in slip plane of DEBG is: (A) 0 (B) 12.6 MPa (C) 37.8 MPa (D) 20.4 MPa

43. It is known that the critical resolved shear stress of a metal is 9 MPa. A polycrystalline

this type of metal contains a large number of grains. Its yield strength is close to (A) 3 MPa (B) 27 MPa (C) 9 MPa (D) 81 MPa

44. A notched sample is tested in tension. At the notch root, the stress concentration factor,

KSC, is 3.5. If the sample yields as a 35 MPa tensile stress is applied, what is the yield strength of the material? (A) 10 MPa (B) 122.5 MPa (C) 35 MPa (D) 31.5 MPa

45. A coil spring is made of a wire, and the wire has a diameter d0. The spring cannot contain

more than n0 turns of coil, and, under a given force F0, the deformation must be larger than a given value, D0. It should carry as much load as possible without yielding of the

A

B

C

D G

H

E

F

wire. To choose the best material for the spring, what is a free variable: (A) the diameter of the spring coil (B) the spring constant (stiffness) (C) the strength of the spring (D) the stress in the spring

46. In the above problem, the performance index should be

(A) σy/G (B) σy

2/G (C) σy

3/G (D) σy

1/2/G

47. In the above problem, among the following candidates, it is most likely that ________ is the best choice. (A) Lead alloy (B) Silica glass (C) PTFE (D) Tungsten (W) alloy

48. A cantilever beam is subjected to a transverse force, F, at the

free end. Its cross section must exactly fit with the square hole on the wall. The hole size is b. The mass of the beam should be around a given value, m0. The force, F, that the beam can support should be as large as possible. To choose the best material for the beam, the free variables include (A) The mass of the beam (B) The length of the beam (C) The strength of the beam (D) The cross-sectional area of the beam

49. In the above problem, the performance index for materials selection is

(A) σy/ρ (B) σy⋅ρ (C) σy

1/2/ρ (D) σy

2/3/ρ

50. In the above problem, among the following candidates, ________ is the best one. (A) Lead alloys (B) Carbon fiber reinforced polymers (CFRP) (C) Tungsten alloys (D) Wood, // grain

F

5.

Figure 14

Figur