华南理工大学机械工程试卷英文

South China University of Technology

School of Mechanical Engineering

Final Exam of Course: Materials for Mechanical Engineering

21 June 2006

Name: ___________ or ______________________ SID: ______________________ Chinese English (Han-Yu-Pin-Yin)

Time allowed: 1.5 hours

Answer 4 Questions in Total. For Q4 (Analysis and Calculation part), where appropriate, include a clear sketch of the problem.

Q1 — Multiple choices (ticking the most appropriate answer, 10 points)

1．In a metal, the forces can be considered as : ________

(a) the attractive forces between electrons & positive ions,

(b) the repulsion between the complete electron shells of the positive ions, &

(c) the repulsion between the positive ions as a result of their similar positive charges.

d. none of the above

2．Properties are affected by: ________

a)Bonding type

b)Crystal Structure c)Imperfections

d)Processing

3. Which of following structure in metals/alloys has a better ductility ?________.

a. FCC c. BCC

b. SC

d. none of the above

4.For a 1% steel the carbon is completely soluble in iron at: ________

a.723 °C c.100 °C

b.1400 °C

d. none of the above

5. In solidification, which of following mechanisms or steps best describing the process?________.

a. cooling and reheating

b. nucleation and growth

c. melting and cooling

d. none of the above

6. Which of the following will have the highest energy? ________.

a. Atom at the grain boundary

b. Atom on surface of a crystal;

c. Atom on surface at the grain boundary

d. Atom in a grain.

7. Engineering alloys can be broadly divided into ________.

a. Ferrous Alloys and ceramic

b. metals and Non-ferrous Alloys;

c. Ferrous Alloys and Non-ferrous Alloys

d. metals and alloy.

8. How many equivalent atoms are there per unit cell for an FCC unit cell?________.

a. 2

b. 3

c. 4

d. none of the above

9. In the Al-20%Cu alloy, does the first solid which forms on cooling contain: ________

a. 20% Cu

c. Less than 20% Cu b. More than 20% Cu

d. No Cu (i.

e. pure Al)

10. In Al-Si die-castings, trace amounts of sodium are added to modify the microstructure and improve properties. The Sodium: ________

a. increases the amount of primary Si c. increases the eutectic temperature

b. refines the eutectic structure d. none of the above

Q2 — Fill out the following blanks (10 points)

1. If some silicon is added (1 to 2%, maybe 3 %) the carbon will tend to graphitize, • and there are various forms the graphite can have. Then, the carbon can also be in the form of graphite ( __ ; __ ; __ ; Spheroidal cast iron)

2. Normalizing (air cooling from austenitizing temperature. Product: fine __ ; Quench (fast cooling from austenitizing temperature in water or oil. Product: __ ; Austempering. (Quench to T above Ms and soak until phase transformation takes place. Product: __ ;

3. Arrange the fracture steps of the tensile specimen: , , , , .

(a) Cavity Formation

(b), Fracture

(c) Necking,

(d)Crack propagation,

(e) Cavity coalescence to form a crack,

4. At room temperature, Strength is . grain size

Q3 — Concept, definition & conclusion: True or false (circling) (5 points)

1. At any particular temperature, the overall rate of transformation is product of the nucleation and growth rates. True or False

2. The general effect of the alloying elements is to retard the softening rate, so these alloy steels will require a higher tempering temperature to obtain a given hardness than carbon steel of the same carbon content. True or False

3. There are naturally occurring vacancies in all crystals; The number of vacancies goes up as the temperature goes up. True or False

4. Adding impurities on purpose is called inoculation. Impurities provide a “seed” for nucleation， In heterogeneous nucleation, solidification occurs on many “seeds”, so the grains are smaller, and more uniform. True or False