ME3251

NATIONAL UNIVERSITY OF SINGAPORE

ME3251 MATERIALS FOR ENGINEERS

(Semester 2 : AY2013/2014)

Time Allowed : 2 Hours

INSTRUCTIONS TO STUDENTS:

1. Please write your Student Number only. Do not write your name.

2. This assessment paper contains THREE (3) questions and comprises FOUR (4) printed pages.

3. Students are required to answer ALL questions.

4. Students should write the answers for each question on a new page.

5. This is an OPEN-BOOK ASSESSMENT. Students are allowed to bring any materials into the examination hall.

6. Programmable calculators are NOT allowed for this assessment.

PAGE 2 ME3251

QUESTION 1

Crankshaft (see Figure 1 on next page) is one of the most important engineering components

especially for high horse-power engines for land and sea transportation. Figure 1(b) shows

the basic construction of a crankshaft. In addition to strength, toughness, the surfaces of the

main journals (which rest and rotate inside the bearings on the engine block) and the crank

pins (also called rod journals, onto which the piston rods are connected via the bolted end cap

and bearing) must also be highly wear resistant. The initial stock is typically hot forged into

the approximate shape of a crankshaft. It is then machined into the desired dimensions

followed by drilling lubricant passage holes into respective crank pins and main journals.

After heat treating to obtain the desired properties, the surfaces of both the main journals and

the crank pins are polished to a fine finish. Such components are typically designed for life.

(a) Discuss the various design requirements of a crankshaft, paying attention to the different functions and stresses experienced and hence design requirements for

different parts (i.e., main journal, crank pin and crank web) of such a component.

(15 marks)

(b) You are to manufacture a batch of crankshaft each of about 1 meter in overall length. Discuss how you would go about materials selection and the key fabrication steps

involved, paying attention to how you would meet the various design requirements for

different parts described in (a) above. (You may ignore the hot forging operation by

assuming that this fabrication step will be subcontracted out).

(15 marks)

(c) Discuss ways that you could use to prevent corrosion of your crankshaft. Provide your choice of corrosion prevention technique and reasons for making such a choice.

(10 marks)

PAGE 3 ME3251

Figure 1(a). Crankshaft and piston rods of an engine.

Figure 1(b). Sketch of a crankshaft showing various key parts.

Figure 1(c). A picture of a finished crankshaft.

Crankshaft

Piston Rod

PAGE 4 ME3251

QUESTION 2

(a) Glass and alumina ceramics are two most commonly used technical ceramics. Discuss

(i) the differences and similarities between their microstructures and properties;

(ii) the concept of tempered glass for toughening of glass plates and why the same concept may not work for alumina ceramics; and

(iii) how you would increase the toughness of alumina ceramics and what properties may be compromised in the process.

(15 marks)

(b) (i) Under what conditions you may consider using ceramic materials in your design instead of metals?

(ii) List key considerations in designing components with ceramic materials

paying attention to their brittle nature.

(15 marks)

QUESTION 3

(a) Describe the impact of polymeric materials in todays society (provide reasons where appropriate).

(15 marks)

(b) Discuss (i) the use of fibre-reinforced polymeric materials as stressed parts in engineering applications and (ii) the major differences in design considerations for

engineering structures made of fibre-reinforced polymeric materials as opposed to

those made of metals.

(15 marks)

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