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The University for businessand the professions

School of Engineering and Mathematical Sciences

All courses

ME2109: Engineering Science 2

Materials and ManufacturePart 2 Examination

xxxxxxxxxxx 2012 xxxx - xxxx

Answer THREE questions only

Number of answer books to be provided: One with graph paper

Calculators permitted: Casio FX-83/85 MS/ES/GT+ ONLY

Dictionaries permitted: None

Additional materials: NoneCan question paper be removed from the examination room: NO

External Examiner:Internal Examiners: Dr R J Goodey


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Question 1

Consider the plate of unit thickness shown in Figure Q1.

a) Assuming the material is elastic and by considering the geometry shown, determine anexpression for the elastic energy released upon formation of the crack, length a.

[10 marks]

b) If the material is brittle then the energy absorbed upon formation of the crack is given by

S = 2a. Use this and the equation determined in Part (a) to sketch a curve showing the

relationship between crack length and energy in the system. Show on this curve how you

would determine the critical crack length.

[10 marks]

c) If material is ductile rather than brittle, discuss the effect this has on formation of a crack.[5 marks]

Fig. Q1

Question 2

There are many choices available for the processing of plastics. The final cost of each plastic

component will be a function of a number of factors. Discuss the influence of these factors on

cost per component. You may wish to consider production method, capital costs, production

volume, material costs and labour costs although this list is not exhaustive.

[25 marks]

pa

a

s

s


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Question 3

Table Q3 shows the influence on the Vickers hardness number of cold working a sample of

copper alloy.

a) Explain the cold working process and how it affects the structure of the copper alloy.What is the practical significance of this process?

[10 marks]

b) By consideration of the results shown in Table Q3, what effect would you expect coldworking to have on the tensile strength and ductility of the copper alloy? On the same

axes, sketch four curves to represent the tensile stress-strain response of each of the

copper alloy samples.

[8 marks]

c) Brittle behaviour is generally undesirable in metal alloys. Explain how annealing canreduce the effects of cold working.

[7 marks]

Percentage cold work Vickers hardness number

0 80

20 135

40 150

60 160

Table Q3

Question 4

a) Explain what is meant by creep in materials. What factors affect the creep rate of a givenmaterial?

[4 marks]

b) Sketch and label a typical creep curve for metal. Indicate the region in which power lawcreep applies.

[4 marks]

c) State 3 components where creep behaviour must be considered during design. For eachapplication explain the effects of creep over the lifetime of the component.

[9 marks]

d) Describe a test that could be performed in the laboratory in order to determine the creepproperties of a material.

[8 marks]


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Question 5

a) Discuss what occurs when a plain carbon steel of the eutectoid composition (0.76wt% C)cools in equilibrium from 800C to a temperature below 727C.

[5 marks]

Figure Q5 shows the isothermal transformation diagram for the same steel alloy discussed in

Part a).

b) Estimate the cooling rate required (starting at 727C) to give a 100% Martensitic steel atroom temperature.

[5 marks]

c) Explain why, in practice, it is not possible to achieve alloys that are 100% Martensite.[5 marks]

d) From Figure Q5, what microstructure will arise if a steel alloy at 727C is cooled rapidly

to 600C, held there for 100s and then quenched to room temperature? [5 marks]

e) Explain why, in general, Figure Q5 is impractical for determining cooling regimes toproduce specific alloys. What may be a more practical way to treat the cooling of metal

alloys?

[5 marks]

Fig. Q5

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