EXAM COVER SHEET
Student name:
Student ID
Campus:
Associate Degree of Applied Engineering
(Renewable Energy Technologies)
Subject number:
ENMAT101A
Subject name:
Engineering Materials and Processes
Semester
1, 2013 Exam A
Time allowed 1:50 hours plus 10 minutes reading time
General instructions
Marks
Write your answers using black or blue pen
Total marks: 25% of Subject
Write your name and campus at the top of
each page
All questions must be attempted.
No liquid paper (whiteout) can be used – if
you make a mistake, just cross out your
attempt.
Marks allocated for each question are shown
throughout the examination paper. Total
marks 100.
Examination aids permitted as indicated
Standard
dictionaries
Bilingual
dictionaries
Technical
dictionaries
Programmable
calculators
Nonprogrammable
calculators
No
No
No
No
Yes
Other examination aids permitted


Writing implements (pens, pencils, erasers, highlighters)
Ruler
Note: Reference information included at end
ENMAT101A Engineering Materials and Processes
Semester 1, 2013
Student name:
Campus:
Question 1 (6 marks total)
(a) Complete the following table. Give the approximate (rounded off) atomic mass unit
values for the three particles that make up an atom. (1 mark)
Particle Name
Atomic Mass Units
Charge
1
+1
(b) Explain the main difference between a nuclear reaction and a chemical reaction with
reference to the simple atomic model (Bohr model). (2 marks)
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(c) Draw the Bohr model representation (in 2d) of an atom of Lithium and one of Fluorine. Show
the correct number of each particle as from part (a). Illustrated what happens when the two
atoms combine to form Lithium Fluoride. Include labels. (3 marks)
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Question 2 (10 marks total)
(a) Explain why an optical microscope cannot see atoms. (1 mark)
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(b) Describe / illustrate a method of “seeing” atoms to form images of an atomic lattice. (3
marks)
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(c) What are Van der Waal’s forces? Illustrate and explain with reference to the table of
properties for Alkanes (see Reference Section at the end). (3 marks)
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(d) Illustrate the atomic structures of a pure metal, and compare to a simple thermoplastic.
Use this to explain the differences in conduction of electricity (3 marks)
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Question 3 (6 marks total)
Give definitions for the following (1/2 mark each = 6 marks)
a) Ductility
______
b) Hardness
______
c) Elasticity
______
d) Stiffness
______
e) Toughness
______
f) Stress
____________
g) Strain
____________
h) Yield strength
______
i) Modulus of elasticity
______
j) Modulus of rigidity
______
k) Creep
____________
l) Resilience
______
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Question 4 (10 marks total)
(a) As-drawn 0.5% carbon steel rod is quenched and tempered to HRC 50. Explain these
three terms and their effect on mechanical properties. (2 marks)
As-drawn:
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Quenched:
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Tempered:
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Using the same axis, sketch typical STRESS/STRAIN curves for the following four materials.
Label the UTS, YS and/or elastic limit. Indicate toughness and stiffness. Use values from
Reference Section. (2 marks each)
(b) Mild steel: Use a dotted line to represent true stress
(c) Grade 8.8 bolt. Indicate toughness
(d) Grey cast iron:
(e) PVC
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Question 5 (7 marks total)
(a) Explain the mechanism of failure for the two specimens shown below with reference to
slip in a metallic crystal lattice. (3 marks)
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(b) Describe the two main ways the yield strength of a metal can be increased. Explain in
terms of both the microstructure and the bulk mechanical properties. Give example
materials in each case. (4 marks)
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Question 6 (12 marks total)
This high performance shaft is made from
hardened alloy steel (as listed in the
Reference Properties).
In the application the nominal stress was
well below the yield strength.
It had been running for some months
before the shaft fractured suddenly.
According to material specifications and
calculations, it was supposed to last for
many years, if not indefinitely.
(a) What type of failure this? (1 mark)
(b) Sketch a generalised S/N curve for steel using the rule of thumb that the endurance limit is
approximately half the ultimate strength. Include an S/N curve for aluminium for comparison.
Label both curves. (2 marks)
(c) Explain why this shaft does not comply with the S/N curve for this material. Use appropriate
terminology. (1 mark)
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(d) What is the difference between fatigue strength and endurance limit? (1 mark)
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(e) Explain and illustrate how shot peening works and give an example of where it would be used.
(2 marks)
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(f) What could happen to a high carbon steel if shot-peening is over-done? (1 mark)
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(g) How could the depth of depth of shot-peening treatment be controlled? (1 mark)
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(h) Explain design changes from that of high strength bolt A and the performance bolt B, with
the goal of improving fatigue resistance. Both have the same length, diameter and thread.
(3 marks)
Design change 1:
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Design change 2:
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Design change 3:
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Manufacturing process change:
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Question 7 (9 marks total)
Give definitions for the following (1 mark each)
a) Dendritic Structure
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b) BCC
____________
c) FCC
____________
d) Allotropy
______
e) Recrystallisation
______
f) Amorphous
____________
g) Explain the difference between melting point and recrystallisation temperature. (2
marks)
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h) What sort of grain-structure problem occurs if heat treatment was done at
excessive temperature and/or for too long? (2 marks)
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Question 8 (7 marks total)
(a) Describe how this grain structure formed on this
aluminium ingot. (Sort the grain structures into 3
groups and explain why there is a cone-shaped
hole at the top) (2 marks)
(b) What is the main cause of porosity in a casting? Describe how this can be
prevented/reduced by the design of the product. (1 mark)
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(c) Describe how porosity can be prevented/reduced by the arrangement of a low
pressure casting process. (1 mark)
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(d) List advantages/disadvantages of each metal casting process listed in the table: Include
melting point, accuracy, setup costs, production costs, design limitations like complex
geometry and size. (1/2 mark each = 3 marks)
PROCESS
Advantages
Disadvantages
Typical metal
Sand Casting
Investment
Gravity die
High pressure
die
Centrifugal
Lost Foam
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Question 9 (9 marks total)
The tensile test was carried out in the sequence from points A to point J.
Data for this test: Material: 0.4% C steel as drawn. Gauge Length: 50mm. Diam 6.02mm
Point
Load (kN)
Elong (m)
A
0
0
B
19.8
188
C
0
9
D
24.8
298
E
0.5
9
F
27.6
756
G
H
27.3
894
J
(a) Sequence A-B-C-D-E: This value is typically calculated at 0.1% or 0.2%. State the value
derived from this test. (1 mark)
_________________MPa (__________%)
(b) Give a value for the elastic limit. (1 mark)___________________________________
(c) Calculate the UTS. (1 mark)______________________________________________
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(d) The rate of travel (stretching/compression) was increased in F-G-H. What effect did this
have on the elastic region, and what is the name of this phenomenon? (2 marks)
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(e) Explain the mechanism of work hardening (at the grain microstructure level) with
reference to any relevant portions of the sequence A-B-C-D-E-F-G-H-J. (4 marks)
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Question 10 (4 marks total)
(a) What specific material property distinguishes hot-working from cold-working
processes? (1 mark)
(b) Compare forming processes. Include melting point, accuracy, setup costs, production
costs, design limitations, strength, size. (3 marks)
PROCESS
Advantages
Disadvantages
Typical metal
Hot rolling
Extrusion
Cold Rolling
Forging
Powder
Metallurgy
Machining
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Question 11 (8 marks total)
(a) Give four reasons for using alloyed metals rather than pure metals. (2 marks)
(b) Describe two diffusion processes and explain how they have the effect of increasing the
strength of a ductile metallic lattice. Give an example of one of these. (3 marks)
(c) The tin/lead phase diagram (Reference Section): What is the word used to describe the
61.9% Sn mixture and what is special about it? (1 mark)
(d) The tin/lead phase diagram (Reference Section): Compare 62/38 solder with 50/50
solder. Which one is more likely for small electrical soldering, and which one for
plumbing work where solder cools more gradually? (2 marks)
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Question 12 (12 marks total)
(a) The above samples were all Carbon steel and cooled slowly. Describe the grain types and
give an estimate of their carbon content. (2 marks)
A.
B.
C.
D.
(b) What is the main difference in the process of normalising of a forging vs annealing of a
casting? (2 marks)
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(c) Describe the cooling of each of the 4 samples above. Plot the cooling process and label
important points to include in your descriptions. (2 marks each = 8 marks)
A.
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B.
C.
____
D.
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REFERENCE SECTION
3
Alkane
Formula
Boiling point [°C]
Melting point
[°C]
Methane
CH4
-162
-182
gas
Ethane
C2H6
-89
-183
gas
Propane
C3H8
-42
-188
gas
Butane
C4H10
0
-138
gas
Pentane
C5H12
36
-130
0.626 (liquid)
Hexane
C6H14
69
-95
0.659 (liquid)
Heptane
C7H16
98
-91
0.684 (liquid)
Octane
C8H18
126
-57
0.703 (liquid)
Nonane
C9H20
151
-54
0.718 (liquid)
Decane
C10H22
174
-30
0.730 (liquid)
Undecane
C11H24
196
-26
0.740 (liquid)
Dodecane
C12H26
216
-10
0.749 (liquid)
Icosane
C20H42
343
37
solid
Triacontane
C30H62
450
66
solid
Tetracontane
C40H82
525
82
solid
Pentacontane
C50H102
575
91
solid
Hexacontane
C60H122
625
100
solid
Density [g·cm ] (at
20 °C)
Tin / lead phase diagram
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