Exam January 2017, questions PDF

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Past exam paper offered for practice as the questions are more or less the same...

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338MAE/4 January 2017 Coventry University Faculty of Engineering, Environment and Computing

338MAE Advanced Materials and Manufacture Instructions to candidates

Time allowed: 2 Hours 0 minutes

Answer: All of Question 1 in Section A and two questions only from Section B The total number of questions in this paper: 4 Start each question on a new page and carefully identify your answers with the correct question number Each question has individual marks shown next to the question Please note: If you answer more than two questions from Section B, only the first two answers will be marked. For this examination you will be supplied with the following: Formulae, where needed, are provided in the question Answer booklet

You may take this question paper away at the end of the examination Please keep in a safe place for future reference

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338MAE/4 Section A Answer all parts of Question 1 Total marks available in Section A = 34 Marks Question 1 a) What do you understand by the term superplasticity with respect to a metal shaping technology for engineering alloys

(2 marks)

For an alloy to be capable of superplasticity, the microstructure needs to be in an appropriate configuration i.

What deformation mechanism does SPF utilise in engineering alloys? (1 mark)

ii.

Discuss the microstructural features that an alloy designed to be superplastically formed should exhibit

iii.

(5 marks)

What are the advantages of SPF for production of complex sheet metal geometries compared with the traditional approach of a fabrication composed of press-worked sub-components (5 marks)

Question 1 continued on next page…

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Question 1 Continued…. b) Ductility can be restored to a cold worked metal by a re-crystallisation annealing treatment i.

With respect to alloy microstructure review the changes that occur in a cold worked material during a re-crystallisation annealing treatment (5 marks)

ii.

If the re-crystallisation annealing treatment is too pro-longed, review what detrimental phenomena may occur to the metal in terms of both microstructure and consequent detriment to ductility

(4 marks)

c) i.

List and explain factors that contribute to poor surface finish during grinding of aerospace alloys?

ii.

(4 marks)

How should one optimise surface finish in grinding operations? (4 marks)

iii.

What is the macro grinding tool wear process? In your answer include a sketch graph of tool wear vs time and indicate the stage at which each wear sub-process occurs (4 marks) (Total 34 marks)

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338MAE/4 Section B Each question in Section B is worth 33 marks Answer two questions only from Section B Question 2 Three candidate materials have been proposed for motorsport connecting rods for racing applications (see table Q2 page 6). The two primary failure modes for connecting rods are buckling in compression and fatigue failure in tension. Therefore, there is a need to design accordingly, taking account of these potential failure modes whilst minimising mass of the connecting rods. The rods therefore need high specific buckling resistance and high specific fatigue strength. A schematic diagram of the connecting rod is shown in figure Q2 (page 5). The breadth (b) of the rod shank cross section is the design free variable, whilst the width (w) is fixed. Length L is fixed Take second moment of area (I) as: I 

b.w 3 12

Euler equation can be used to define the critical buckling load FCRIT 

 2 .E.I L2

Where: E= Elastic modulus Take Mass = w.b.L.ρ Maximum compressive load = FCRIT Maximum tensile load = FMAX

Question 2 continued on next page…

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Question 2 continued…

Figure Q2: Schematic of connecting rod a) Derive an expression for the mass of the rod that contains a performance index for specific buckling resistance, the performance index in the derived for expression for the mass being in the form to be minimised

(12 marks)

b) Derive an expression for the mass of the rod that contains an expression for specific fatigue strength, the performance index in the derived for expression for the mass being in the form to be minimised

(4 marks)

c) For each candidate material (see table Q2 page 6 for listing and properties) calculate the material performance index in the form it is to be maximised for i.

Specific buckling resistance

(6 marks)

ii.

Specific fatigue strength

(6 marks)

d) Hence justify selection of the optimum material based on maximising both performance indices

(2 marks) Question 2 continued on next page…

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338MAE/4 Question 2 continued…

e) Reviewing material property data from table Q2, briefly discuss any potential issue with the optimum material as defined by maximising both performance indices

(3 marks)

AISI 1060

A201 (T7)

Mg-Z6-15%SiC(P)

Medium Carbon

Aluminium Alloy

Mg alloy Metal Matrix

Steel

(Solution treated,

Composite

(Normalised)

quenched &

(silicon carbide

stabilised)

particulate-15% by volume)

Elastic Modulus

210 x 109

70 x 109

72 x 109

331 x 106

97 x 106

102 x 106

7800

2780

2030

70

24

12

(N.m-2) Fatigue strength @ 107 cycles ( N.m-2) Density (Kg.m-3) Fracture Toughness (MPa.m0.5) Table Q2. Candidate materials and properties (Total 33 marks)

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338MAE/4 Question 3 The iron-carbon phase diagram is shown in Figure Q3A (page 8) for your reference a) In relation to furnace cooling of a 0.8% carbon steel after austenitisation at 780C, describe the eutectoid transformation that occurs in plain carbon steels at ~727C and the resultant microstructure after the transformation (6 marks)

b) One of the most important heat treatments is the hardening of steels by quenching from the austenite phase region to generate a phase called martensite. Review the nature of the austenite to martensite transformation (assume a 0.5% carbon steel), explaining: i.

How quenching supresses the eutectoid transformation (5 marks)

ii.

The microstructure and consequent mechanical properties of the medium carbon steel in the as quenched condition

iii.

(3 marks)

Explain what property characteristic can be restored to a medium carbon steel (e.g. 0.5% carbon) in the as quenched condition upon tempering by discussing the microstructural changes that occur during tempering: a)

At 150 ◦C

(3 marks)

b)

At 500 ◦C

(3 marks)

c) Certain very high strength steels can be susceptible to the phenomena of tempered martensite embrittlement when tempered in the rage 300-400°C. What is the cause of this phenomena?

(2 marks)

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338MAE/4 Question 3 continued…

Figure Q3A. Iron - Carbon phase diagram

d) The Al-Cu phase diagram is shown in Figure Q3B (page 9) for your reference. For the ageing of an Al-Cu alloy of composition X (marked on figure Q3B), after solution treatment and quenching:

i.

Sketch a graph of yield strength vs time assuming ageing at 150C and explain the strengthening mechanisms that contribute to the overall enhancement in yield strength during the ageing process. (8 marks)

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ii.

What do you understand by the term intermediate working as applied to age hardenable alloys prior to the final ageing stage of the heat treatment? Indicate how the process of intermediate working can give a further enhancement in yield strength

(3 marks)

Figure Q3B. Partial Al-Cu phase diagram

(Total 33 marks)

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338MAE/4 Question 4

a) Discuss the mechanism by which Laser Shock Peening (LSP) introduces residual stresses into a metallic material. Use diagram(s) to sketch the laser beam workpiece material interaction zone and the residual stress profile induced in the work piece

(10 marks)

b) Figure Q4 (page 11) shows variation of fatigue crack growth rate (da/dN) as a function of crack length for a laser peened and an unpeened turbine blade. Determine the fatigue crack growth rate when the crack is 2 mm long, and from the result, comment on the conditions for which the crack grew more slowly and explain why.

(4 marks)

c) What advantage does LSP have with respect to traditional mechanical shot peening

(2 marks)

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Figure Q4. Fatigue crack growth rate (da/dN) vs. crack length

d) Name four types of chemical reaction in Chemical Vapour Deposition (CVD) processes and give their generic equations.

(8 marks)

e) Explain the advantages and disadvantages of atmospheric CVD, Low pressure CVD, and plasma enhanced CVD

(6 marks)

f) List one practical examples of each process listed in part d) above (3 marks)

(Total 33 marks)

End of Paper

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