advance materials

ANSWER ALL QUESTIONS

QUESTION A1

(i) The British Plastics Federation (BPF) is the world's longest running plastics trade association, established in 1933 to represent the UK industry. BSF want to support the education institution along with the industrial partner to support the setting up the polymer laboratory in the universities. In the process of setting up the injection moulding machine in UCLAN a trial experiment was conducted on the thermosetting plastics. A force, F will inject a given weight of an epoxy thermosetting polymer into intricate mould of the injection moulding machine in two different time and temperature scale, i.e., 30 s at 180 degrees Celsius and in 85 s at 162 degrees Celsius. If the viscosity of the epoxy thermosetting polymer follows an Arrhenius law of diffusion, with a rate of process proportional to

𝑄𝑄 2 s-1,

exp − m

𝑅𝑅𝑅𝑅

calculate how long the process will take at 237 degrees Celsius.

(6 marks)

(ii) Discuss the possible behaviour of this material in relation to creep and compare it with the possible behaviour of a thermoplastic taking into consideration the main polymer structure characteristic of both. Compare the equation to model the injection with the equation to model creep.

(4 marks)

[Hint] Give you answers with no more than 3 decimal places.

(Total: 10 marks)

QUESTION A2

(i) The phase diagram for the Al - Si system (the basis of aluminium casting alloys) is shown in Figure 1. Explain what is happening when the alloy Al – 30 wt % of Si is cooled from 900 ℃ to room temperature. You need to consider phase

transformation, microstructure changes, temperatures, and composition.

(6 marks)

Figure 1: Phase Diagram of Al - Si binary system

(ii) You have been asked to calculate the critical nucleus radius, r* and the activation free energy ∆𝐺𝐺∗ for the solidification of pure nickel if nucleation is homogenous. The latent heat of fusion and surface energy of nickel are given as -2.53 x 109 J/m3 and 0.250 J/m2 respectively. The supercooling curve value for nickel is 319 ℃. The melting temperature of nickel is 1455 ℃.

(4 marks)

(Total: 10 marks)

QUESTION A3

CASE STUDY ANALYSIS

Critically assess the outputs, techniques and reported failures on these two case studies (800 words maximum):

1. Failure analysis of a failed connecting rod cap and connecting bolts of a reciprocating compressor, X. Zhu, J. Xu, Y. Liu, B. Cen, X. Lu, Z. Zeng, Engineering Failure Analysis,

Volume 74, 2017, Pages 218-227, ISSN 1350-6307, https://doi.org/10.1016/j.engfailanal.2017.01.016.

( http://www.sciencedirect.com/science/article/pii/S1350630716307488 )

2. Failure analysis and fatigue performance evaluation of a failed connecting rod of reciprocating air compressor, M. N. Ilman, R. A. Barizy, Engineering Failure Analysis,

Volume 56, 2015, Pages 142-149,ISSN 1350-6307, https://doi.org/10.1016/j.engfailanal.2015.03.010.

(http://www.sciencedirect.com/science/article/pii/S1350630715000989)

[Hint 1]: In order to do this task successfully, you will need to read other case studies from the same journal and from books and investigate the techniques, structures and failures named in the articles but not explained, as it is assumed the reader already knows about them.

[Hint 2]: In order to understand the articles, you will need to find out the meaning of the technical terms used. You will be expected to use suitable technical terms as part of your analysis.

[Hint 3]: You can discuss for example failure modes or materials phases. You may discuss alternative techniques to be used in order to verify the outcomes of the authors. Is there any other technique could have been considered not currently included in the article? What could have been the benefit? Why do you think those techniques have been used in the article? [Hint 4]: Was it possible to anticipate the failures in the process design? Might a good Finite Element Method analysis have predicted the failures?

[Hint 5]: Use references, examples and/or your own experience appropriately.

(20 Marks)

SECTION B

ANSWER ALL QUESTIONS

QUESTION B1

MATERIAL SELECTION FOR A RIPPER

Select the material for a ripper to be used in a bulldozer. The ripper works as a beam with a distributed load. The maximum working depth of the ripper is 0.6 m and the maximum load is the traction force of the bulldozer (60 kN). Figure 2 shows views of both ripper and bulldozer as well as simplified view to be used in this exercise. This is an open exercise.

(a) (b) (c)

Figure 2: (a) ripper’s view, (b) schematic simplified diagram of ripper, (c) bulldozer view.

You will need to decide extra constraints and find out the equations for a beam. You will need to decide your objective and to compare the results with real world materials. You will need to translate the problem, derive the performance index or indexes, select some screening constraint and select the actual material graphically.

You have to document the whole selection process.

[Hint 1]: You may select materials with minimum mass or minimum cost or both as your objective. You will have to decide your own dimensions for the ripper and the constraints.

[Hint 2]: 20 percent of the total mark for this question will be assessed for the clear definition of the problem and for writing down the necessary equations used in the problem.

[Hint 3]: 40 percent of the total mark for this question will be assessed for the derivation of the material index with correct material performance equation.

[Hint 4]: 40 percent of the total mark for this question will be assessed to the use of GRANTA EduPack for the material selection.

Reminder , as it is an open exercise, each student is expected to have a unique solution as definition of the problem will be unique.

(Total: 30 marks)

QUESTION B2

CPE Pressure Vessels Limited Company manufacturers pressure vessel for oil, gas, petrochemical, nuclear and water industries as shown in Figure 3 (length L, diameter 2R, hemispherical ends). As a design engineer of the CPE company you have been asked to design a pressure vessel for the food manufacturing industry. The main objective of the work is to select a suitable material for the outer wall of the pressure vessel. When the pressure vessel is fully assembled it resemble as a cylindrical shape having an external pressure, p. The design of the outer wall of the cylindrical pressure tank and the selected material should resist the external pressure. The radius of the pressure tank is 10 m. The outer wall containing the pressure, p should not fail either by yielding or by fast fracture. The size of the possible largest crack contained in the outer wall is ac.

Figure 3: Pressure vessel for the food manufacturing company

Most of the pressure vessels are made of high strength alloy steel, and they are heavy. You are asked to explore the potential of alternative materials for lighter pressure vessels, recognizing there must be a trade-off between mass and cost - if it is too expensive, the manufacturing company will not want it even if it is lighter.

Materials properties that are available for ranking materials are: density (ρ); Yield strength (σy); Critical stress intensity factor or fracture toughness of the material (𝐾𝐾𝐼𝐼𝐼𝐼). The volume of material can be evaluated with respect to the surface area and the thickness of the cylindrical outer wall.

You will need to decide your own dimensions, extra constraints and find out the equations for yielding and fast fracture of the pressure vessel. In order to translate the right material selection for the food processing application into a real engineering problem you need to answer the following questions:

(a) Translation of problem indicating function, objective, constraints and free variables? You need to provide a clear definition to the problem.

(6 marks)

(b) Derive the performance material index for failure and select materially graphically. Discuss the implication of two performance index for the selection of one material.

(10 marks)

(c) Explain and justify with supporting evidence (both numerical and graphically) what would happen to the performance index if both the ends of the pressure vessel are closed.

(10 marks)

(d) Show that the mass and material cost of the pressure vessel relative to one made of high strength alloy steel is given by

𝒎𝒎 𝝆𝝆 𝝈𝝈𝒚𝒚,𝟎𝟎 𝑪𝑪 𝑪𝑪𝒎𝒎𝝆𝝆 𝝈𝝈𝒚𝒚,𝟎𝟎

= and =

𝒎𝒎𝟎𝟎 𝝈𝝈𝒚𝒚 𝝆𝝆𝟎𝟎 𝑪𝑪𝟎𝟎 𝝈𝝈𝒚𝒚 𝑪𝑪𝒎𝒎,𝟎𝟎𝝆𝝆𝟎𝟎

(4 marks)

where ρ is the density, σy the yield strength and Cm the cost per kg of the material, and the subscript “o” indicates values for high strength alloy steel.

[Hint] Use the ratio for new material over the steel.

m

= mass relative to high strength alloy steel m0

C

and = cost relative to high strength alloy steel. C0

Reminder, as it is an open exercise, each student is expected to have a unique solution as definition of the problem will be unique.

(Total: 30 marks)

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