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Materials Engineering and Manufacture
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No.
CITY UNIVERSITY
SCHOOL OF ENGINEERING AND MATHEMATICAL SCIENCES
MEng/BEng Mechanical, Automotive and Motorsport, Energy
Engineering
BSc Automotive and Motorsport Technology
PART II EXAMINATION
Materials Engineering and Manufacture
[ME2103]
Examiner: Dr. J. Busfield
External Examiner: Professor R Crookes
DATE: May 2007 TIME:
Answer THREE out of SIX questions
Page 1 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Question 1
a) Using suitable sketches explain the difference between a force versus deflection
graph and an engineering stress versus engineering strain graph and explain what you
can measure if you integrate each curve? In the elastic region what is the slope of each
graph? Your answers should identify the appropriate units throughout. [7 marks]
b) Sketch typical stress strain curves for each of the following materials:
i) a metal,
ii) a ceramic, and
iii) a polymer. [9 marks]
c) Using key features of these stress strain curves, contrast the typical relative
mechanical properties of each type of material, making specific reference to their
typical elastic modulus, strength, ductility behaviour explaining with examples why
they can be used in particular applications. [9 marks]
Page 2 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Question 2
a) Define the material properties, toughness, GC and fracture toughness, KC. Include
the appropriate units in your answer. [8 marks]
b) A metal strip is subjected to a tensile stress. The strip of metal is 40mm wide and
5mm thick. It contains a sharp edge crack, 3mm long. Assuming that fracture
mechanics applies, if the strip of metal is loaded in tension, at what stress and hence at
what force will it fail and will the failure be a ductile or a brittle fracture? The tensile
strength is 650MPa, the yield strength is 450MPa and the fracture toughness is
50MPa.m1/2. [10 marks]
c) The energy balance for fast fracture is given as
δW ≥ δU + Gc tδa .
where W is the external work applied to the system, U is the internal stored energy, t
is the sample thickness and a is the fracture or flaw size. Derive a relationship from
this equation to calculate the toughness of the adhesive that is used when you unpeel
sellotape from the roll at steady rate by a weight of mass, M attached to the free end
(see figure below). Hence calculate the value for toughness for a roll of width 20mm
which starts to unravel when a mass of 1kg is attached. For this calculation assume
that the acceleration due to gravity, g is 10msec-2.
[7 marks]
Page 3 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Question 3
a) Use the following table and graph of force /kN versus deflection /mm to create a
graph of engineering stress versus engineering strain measured using a screw driven
mechanical tensile test machine. The thicker line with the data points is the result
measured when the sample is tested in the machine, the second thinner line is a
measure of the machine stiffness in isolation. The sample had an original length of
35mm and a circular diameter of 6mm. Your calculations should account for the
machine stiffness, and compensate for the initial slack in the test so that the true origin
is calculated correctly. Show all your workings in the answer booklet. [12 marks]
b) From your graph indicate values for the yield strength, ultimate tensile strength and
the elongation strain to break. [7 marks]
Sample Stiffness
18
Deflection Force
/mm /kN 16
0.00 0.00 14
0.31 0.25
0.56 0.56 12
Force /kN
0.75 1.13 10
1.72 6.56
2.19 9.25 8
2.38 9.50 6
2.53 9.94
4.13 13.56 4
5.19 15.00 2
6.75 15.94
8.13 16.25 0
10.44 15.00 0 2 4 6 8 10 12
11.88 11.56 Delection /mm
Machine Stiffness
Deflection Force
/mm /kN
0.00 0.00
0.31 0.25
0.56 0.56
0.75 1.13
2.53 16.25
c) Identify three ways in which a metal can be strengthened and explain briefly for
each how the increase in strength is achieved. [6 marks]
Page 4 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Question 4
At modest production volumes a 0.25kg aluminium component can be manufactured
by either machining from solid or sand casting. At this stage it is not known from
your marketing department the precise production quantities but you have been asked
to calculate the total cost per part of manufacturing 100, 1000, 10000, 100,000 and
1,000,000 by both processes. To simplify the calculation the capital and labour costs
are assumed to be the same and can be ignored. The following information can also be
assumed:
Aluminium material cost - £7.00 /kg
The waste material created per part by machining - 0.20kg.
The amount of waste material created per part by casting - 0.02kg.
The tooling costs dedicated for machining this part are - £5000.
The tooling costs dedicated for casting this part are - £25,000.
a) Plot an appropriate graph to compare the cost per part for both manufacturing
routes over the entire range of manufacturing volumes. [15 marks]
b) Which is the most cost effective route for low production volumes and what is the
break even point at which the other production process becomes more cost effective
per part? [5 marks]
c) If the product was successful and you were now expecting to be able to sell
5,000,000 parts per year, which alternative manufacturing route not considered so far
would you now consider for manufacturing this product? Justify your choice with
reference to the capital costs and the labour costs as well as by considering the
possible productivity rate of your chosen processing route. [5 marks]
Question 5
a) Identify the most suitable processing technique that should be used to make a large
brass bell for use in a church. Use a suitable sketch to help define the key features of
this process. [8 marks]
b) Identify the most suitable processing technique that should be used to make a
lightweight glass fibre–epoxy resin composite hull for a luxury 8 person cruising boat.
Use a suitable sketch to help define the key features of this process. [9 marks]
c) Identify the most suitable processing technique that should be used to make a
rubber earthquake bearing used to support large civil engineering structure frequently
found in earthquake zones like California or Japan. Use a suitable sketch to help
define the key features of this process. [8 marks]
Page 5 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Question 6
An oar or rowing blade can be considered to be a strong, light, stiff beam that is
loaded in bending. A basic requirement is that it must carry the bending moment
exerted by the oarsman without breaking. Its stiffness is measured by hanging a
weight of 10kg on the oar, 2.05m from the collar and the deflection at the point of
loading is measured, as shown below.
a) Assuming that the oar is of uniform cross sectional area, A, has a length L, and a
second moment of area, I. The denisty of the material it is made from is ρ. What is the
mass, m of the oar? [2 marks]
b) Assuming that the deflection of a simply supported beam, D when it is subjected
to a load F is
FL3
D=
C 1EI
calculate the stiffness of the beam S. [2 marks]
2
A
c) For a circular cross section I = . By eliminating the cross section area, A derive
3π
an equation for the mass of the oar and from this identify the materials index that will
give the most suitable materials for use as a competitive oar. [6 marks]
d) Using the supplied Ashby diagram highlight the most suitable materials from a
range of materials classes that can be used as a minimum mass for the oar.
(Remember to hand the diagram in at the end of the examination) [6 marks]
e) Identify in a table the top five materials for use as an oar from the Ashby diagram
given. Calculate the materials’ index for that material and describe the suitability of
the materials selected for use as an oar with consideration of other factors. [9 marks]
Page 6 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
Information sheet for use with Question 6 – attach with string to you answer booklet
Student identification number: …………………………
Page 7 of 7
ME2103 MaterialsEng & Manufacture_May07.doc
