MECH 390 - PRACTICE 1 – FALL 2011 – SEC 51,52,03

Name:___________________________ Student Number:_______________________

1. Which of the following materials may form crystalline solids?

A.Polymers

B.Metals

C.Ceramics

D.All of the above

E.None of the above

2. The drawing below represents the unit cell for which crystal structure?

A.Simple cubic

B.Face-centered cubic

C.Body-centered cubic

D.Hexagonal close-packed

5. If the atomic radius of a metal that has the face-centered cubic crystal structure is 0.137 nm, calculate the volume of its unit cell (in nm3).

6. For a metal that has the body-centered cubic crystal structure, calculate the atomic radius (in nm) if the metal has a density of 7.25 g/cm3 and an atomic weight of 50.99 g/mol.

7. For the face-centered cubic crystal structure:(a) How many atoms are associated with each unit cell?(b) What is the coordination number?(c) What is the atomic packing factor?

8. What is the difference between atomic structure and crystalline structure.

9. It is possible to produce a perfect crystalline solid that does not contain any vacancies.

A.True B.False

10. The solute is an element or compound present in the greatest amount.

A.True B.False

11. Calculate the fraction of atom sites that are vacant for silver at 661°C. Assume an energy for vacancy formation of 0.63 eV/atom.

12. The number of vacancies in some hypothetical metal increases by a factor of 5 when the temperature is increased from 1070 K to 1180 K. Calculate the energy for vacancy formation (in J/mol) assuming that the density of the metal remains the same over this temperature range.

13. For an alloy that consists of 37.7 wt% Pb and 62.3 wt% Sn, what is the composition (a) of Pb (in at%), and (b) of Sn (in at%)? The atomic weights for Pb and Sn are 207.2 and 118.7 g/mol, respectively.

14. For an alloy that consists of 94.6 g copper, 113 g zinc, and 8.36 g lead, what are the concentrations (a) of Cu (in at%), (b) of Zn (in at%), and (c) of Pb (in at%)? The atomic weights for Cu, Zn, and Pb are 63.55, 65.39, and 207.2 g/mol, respectively.

15. Gold forms a substitutional solid solution with silver. Calculate the number of gold atoms per cubic centimeter (in atoms/cm^3) for a silver-gold alloy that contains 21 wt% Au and 79 wt% Ag. The densities of pure gold and silver are 19.32 and 10.49 g/cm3, respectively, and their respective atomic weights are 196.97 and 107.87 g/mol.

16. Two metal specimens, A and B, have ASTM grain size numbers of 3 and 8, respectively. Which specimen has the larger grain size?

A. B.

17. A fatigue test was conducted in which the mean stress was 70 MPa and the stress amplitude was 210 MPa

A. Compute the maximum and minimum stress levelsB. Compute the stress ratioC. Compute the magnitude of the stress range

18. A steel bar (1045 steel) is subjected to a repeated compression-tension stress cycling along its axis. If the amplitude is 66700 N, find the minimum allowable bar diameter to assure fatigue will not occur by a safety factor of 2.

19. A specimen 101.5 mm long of a low carbon-nickel alloy is to be exposed to a tensile stress of 70 MPa at 427C. Determine its elongation after 10,000 h. Assume that the total of both instantaneous and primary creep elongations is 1.3 mm.

L(103K-log hr)

Str

ess

, ks

i

100

10

112 20 24 2816

data for S-590 Iron

20

20. A cylindrical specimen of some alloy 8mm in diameter is stressed elastically in tension A force of 15700 N produces a reduction in specimen diameter of 5 x 10-3 mm. Compute Poisson’s ratio for this material if its modulus of elasticity is 140GPa.

21. Creep stress rapture is given by the equation: . Find the time to rapture when stress =100

ksi.

22. Tensile stress-strain behavior for an alloy steel is shown in the Figure below. List the following material parameters:

A. Yield strength (0.2%offset) in MPaB. Ultimate tensile strength in MPaC. Total percent elongation (%EL)D. Proportional pointE. ToughnessF. Resiliance

20. A cylindrical specimen of a brass alloy 10.0 mm in diameter and 120.0 mm long is pulled with a force of 11,750 N; the force is subsequently released.

a. Compute the final length of the specimen at this time. The tensile stress-strain behavior is shown below.

b. Compute the final length when the specimen is pulled with a load 23,500 N and then released

23. Using the data represented in Figure 6.19, specify equations relating tensile stress and Brinell hardness for brass and nodular cast iron similar to equations 6.20a and 6.20b for steels.

24. Consider an alloy that initially has a uniform carbon concentration of 0.25 wt% and is to be treated at 1020oC. If the concentration of carbon at the surface is suddenly brought to and maintained at 1.25 wt%, what is the carbon content 0.5 mm below the surface after 8 hours? The diffusion coefficient for carbon in iron at this temperature is 1.6 ×10-11 m2/s;

assume that the steel piece is semi-infinite. Non-steady state diffusion is given by:

C(x,t) Co

Cs Co

1 erfx

2 Dt