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The Bloodhound Supersonic Car (Figure 1a) is a land vehicle that is being designed to achieve 1000
MPH and break the current speed record. The design of the wheels is not easy, they need to withstand
the enormous centrifugal forces turning at very high speed. A normal racing car wheel will just burst.
The approach is to make them of a solid machined metal (Figure 1b).
Figure 1a: 3D view of Bloodhound Supersonic Car
@bloodhound_lsr
Figure 1b: Metal Wheel
@bloodhound_lsr
The stress in the rotating wheel is given by:
𝜎𝜎=𝜌𝜌𝑅𝑅 2𝜔𝜔2
2
Where 𝜌𝜌 is the density, 𝑅𝑅 is the radius of the wheel and 𝜔𝜔 is the angular velocity.
a) Show that given a traveling speed (1000 MPH = 447 m/s) the maximum stress of the wheel
does not depend on the radius of the wheel. Explain why.
(6 marks)
b) Derive a material index for the selection of a material for this application. Use suitable
mechanical properties to do so. The table catalogues the requirements.
(6 marks)
Objective • Maximize the traveling (linear) speed.
Constraints • General dimensions are fixed
• It must not burst
• Adequate toughness to give crack tolerance.
Free variables • Choice of material
c) Select graphically the material in the suitable graph.
(6 marks)
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QUESTION 2
The Strait of Gibraltar crossing is a hypothetical bridge or tunnel spanning the Strait of Gibraltar
(about 14 km or 9 miles at its narrowest point) that would connect Europe and Africa. There have
been many studies about the feasibility and cost of the tunnel since 1979. In 2021 the UK, Spain
and Morocco have announced plans to return to the project (Figure 2).
You are requested to select a material for the walls of the tunnel following the method that we
have seen in the lectures. It is going to be built with a tunnel boring machine. It is surrounded by
high pressure deposits. It needs to withstand an external pressure without failure. It also needs
to be as cheap as possible since the main burden is the cost of the infrastructure.
You need to follow the selection of materials process seen in the lectures and you will need to
define constraints, free variables, objective, function… Note that not everything is given in the text
above and you will need to make your own documented decisions.
Figure 2: (a) view toward Gibraltar, (b) undersea rail tunnel, (c) tunnel digger, (d) satellite view of
potential Gibraltar crossing
You have to document the whole selection process.
(a) Using the above information and your own assumption (if applicable), translate the problem
(4 marks)
(b) From your translation, derive the performance index.
[Hint] Pending on your own assumptions, you may have more than one performance index
(10 marks)
(c) Use Granta Edupack 2021 software to create a graph representing the material index and
identify the region of the chart with the cheapest materials for the tunnel.
[Hint] Pending on your own assumptions, you may have more than one performance index
(d) Select one of the suitable material highlighted in you material selection and compare your
material choice with actual materials used in similar tunnels.
(4 marks)
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QUESTION 3
A crack with a depth of 2 cm is found in a cast iron rod of an old steam engine. Every weekend
the machine is used for 8 hours for demonstration purposes, during which it is run at 15 rpm and
the load in the rod varies from +6.4×104 N to -6.4×104 N. It may be assumed that the crack is
completely closed under compressive load but that under tensile load crack closure is negligible.
The Paris relation is sufficiently accurate until failure.
To answer the following questions, you have been given the following:
Kc = 16 MPa m0.5 ∆Kth = 5
MPa m0.5 cross section rod
= 0.04 m2
factor in the Paris relation: C = 4.3×10-8 m(MPam0.5)
-4
KI = 1.12 σ (πa)
0.5
a) Using the above information, justify if it is safe to use this machine for demonstrations and
if so for how long?
(7 marks)
b) If the load varies from +0.92 MN to -0.92 MN, would it be safe to use the machine and for
how long
(3 marks)
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QUESTION 4
a) Using appropriate drawings, examples and references justify the following statement: “
Creep mechanism “bulk diffusion” is highly dependent with stress”.
(2 marks)
b) Using appropriate drawings, examples and references justify the following statement:
“Creep mechanism “bulk diffusion” is highly dependent on grain size”.
(2 marks)
c) Using suitable examples and references explain what mechanism of creep can be
prevented using a single crystal part.
(2 marks)
d) Using suitable examples and references explain what mechanism of creep can be
accentuated with alloying elements.
(2 marks)
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QUESTION 5
Blackpool Tower has developed problems of corrosion as seen in Figure 3. The corroded parts
must de replaced by new parts made of the same material as the original parts.
Suggest two strategies that can be used to prevent or reduce the corrosion of Blackpool Tower
after the replacement of the corroded components.. You need to justify your choice with examples

Figure 3 : Corroded parts http://www.amteccorrosion.co.uk/
Suggest two strategies (4 marks)
Justify with examples (2 marks)
Discuss (4 marks)
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QUESTION 6
a) Modern bicycle frames are made with aluminium ALU 6061, which tend to crack after years
of use. Whereas steel frames may last decades and never fail. Contrast the behaviour of
aluminium versus steel subjected to many cycles of stress.
(5 marks)
b) Using the information seen in class and suitable examples or references, contrast
Aluminium grade 6061T0 with Aluminium grade 6061T6
(2 marks)
c) Explain the process to transform Aluminium 6061T0 into aluminium 6061T6
(3 marks)
d) Bike users, often ask ,if their cracked aluminium frames can be repaired. Commonly, cracks
appear on the weldments (Figure 4). Peter suggested that it would be easy to weld again by
grinding the crack, expose new base material and weld again on the new material. However,
Peter’s approach is never advised. Discuss one reason why this is advised against from the
structural point of view.
(5 marks)
Figure 4: Cracks located along weld. https://www.mtbr.com/attachments/2016-04-25-
jpg.1066277/
e) Aluminium grade 6061 T6 is shown in Figure 5, indicate three features that are clearly seen in
the picture.
(3 marks)
Figure 5: Metallography of aluminium grade 606 T6
f) Make a drawing of the microstructure of aluminium of the previous question after being
subjected to a heat treatment to reach microstructural phase equilibrium.
(2 marks)
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QUESTION 7
A forklift (Figure 6) has failed. Some researchers have investigated the root cause of the failure
and presented the outcome of the investigation in a research article.
Figure 6: Forklift
George Pantazopoulos, Athanasios Vazdirvanidis, Andreas Rikos, Anagnostis Toulfatzis,
Analysis of abnormal fatigue failure of forklift forks,
Case Studies in Engineering Failure Analysis,
Volume 2, Issue 1,
2014,
Pages 9-14, ISSN 2213-2902,
https://doi.org/10.1016/j.csefa.2013.12.00
5
()
Although the alloy of the fork is heat treatable as stated clearly in the article,
“the forks are made of a common structural steel grade 34Cr4 (W.Nr. 1.7033), see Table 1 [5].
This steel grade is a heat treatable alloy commonly used as a machine element in axle and shaft
fabrication.”
the authors do not include the heat treatment as one of the recommendations given in the
“Conclusions and recommended actions”. Discuss why the authors do not recommend the heat
treatment and justify your answer with relevant data.