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MECH0007 Fundamentals of Materials
Summary of BCC questions & answer hints
Below, you will find a summary of all the BCC questions that were posed in the sync
sessions that we held, and some additional ones to make up 14 - from which you can
choose any 4 to tackle, provide answers to, and submit. I’ve also added in relevant clues
that I might have mentioned in the sync sessions, just in case these were missed or not
clear from the recordings.
There is an exemplar answer given for one question, at the end of this document – so you
can get an idea of the sort of length we are expecting. This is therefore excluded from the
14 you can choose from!
Answers can be up to 1 side of A4 long ideally, including any images or illustrations that
you wish to add in. There is no set format – just try to answer the questions as if they were
encountered in a written exam – a few short paragraphs that provide some background to
the question, detail your answer, and perhaps some illustrations, images or diagrams to
back things up.
Remember, “a picture can save a thousand words”, particularly for an engineer!
You may insert data or images which you obtain from a variety of sources including the
Internet, digital books, or the ppt presentations that were created for this module. It is good
practice to acknowledge where you got such illustrations, by referencing, but you are being
graded on content – not on presentation.
Although the answers to these questions can all be found in the Detailed Notes, the BCC
questions are designed to make you think a little deeper than just a straightforward reading
of those notes. Using other resources, such as some of the books in your bibliography, or
online, will be beneficial in many different ways.
Read the clues given here carefully – whilst they are not the complete answer, they are
generally a lot more comprehensive than just “clues”. If you are particularly stuck on a
question, either find another to work on, or email Dr Wojcik for more help.
Grading is based on correctness and comprehensiveness of the answer, and will be either
A, B, or C (worth 100, 60 or 40 marks respectively, or 0 if no submission is made). One
mark will then be awarded, calculated as the average of the four.
After the deadline (26th April 2021) a booklet of worked solutions will be provided to give
you some formative feedback.
Submission is via the portal under the Assessment tab on the MECH0007 Moodle pages.
Please submit your four answers as a single document, preferably a PDF.
Make sure you put your name on the first page, or your student number.
Q1. How many materials go to make up a typical domestic lightbulb?
A1. See the exempla answer at the end of this document. The answer required a few
paragraphs of text and a diagram. If you need more space for an answer, you can use
more, but do try to keep it to one page per question maximum.
Q2. What properties are required for the material used for a gas turbine blade?
A2. To answer this fully, you need to think about the conditions in the environment in
which the material is being used – what is it like in a jet engine? In the turbine, gas
temperatures can exceed 1200 DegC, so any metal in there needs to have a high melting
point, for example – this cuts out materials such as aluminium alloys. However other
metals that have much higher melting points, such as steel are still unsuitable – why? In a
word you need to consider “oxidation” too. Additionally, there is a phenomenon known as
creep, which all materials suffer from where, at temperatures approaching an appreciable
fraction of their melting point, they begin to suffer time dependent deformation, when under
load. Aside from this, other more traditional selection criteria such as strength (but at high
temperature) and density, will also play a part.
Q3. Given that bonds in both ionic and metallically bonded solids are non-directional and
hence allow atom layers to easily move over each another, why are metals so much more
ductile than ionic solids (e.g., common salt)?
A3. The clue to this one is to understand how the atoms (or more correctly ions) are
organized in both metals and ionic solids. In a metal, the metallic bond means all the ions
are of the same type – negative. Sliding (the process of slip at the core of plastic
deformation) one plane of these ions over the other is relatively easy – and does not result
in a change to the crystal structure or failure of any bonds (given they are all
omnidirectional electrostatic bonds) – so the material doesn’t actually facture. This is
similar for the ionic bond, except that slip is more difficult because of the disruption it
causes to the electrostatic fields – think about the signs of the ions. Slip can happen, in
theory, but the stresses required are so close enough to those actually needed to break the
bonds, that fracture tends to happen first.
Q4. Can you mathematically infer that the toughness of a material is related to the area
under the stress-strain curve?
A4. If you assume that toughness defined as the work done in fracturing a material, then
you need to define work in terms of the stress-strain curve. If work is defined as force x
distance, then it is a simple enough proof to show that this is related to the area under the
stress-strain curve. Care must be taken however in defining what area – as the work done
in most materials is a combination of elastic deformation and plastic deformation. The
elastic work is usually returned to the system when fracture occurs.
Q5. Why is it so difficult to make amorphous (glassy) metals?