associate degree of applied engineering (renewable …€¦ · web viewgeneral instructions. marks....

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 indicatedStandard dictionaries

Bilingual dictionaries

Technical dictionaries

Programmable calculators

Non-programmable 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 1

Charge +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)

© TAFE NSW Higher Education 2012Version: X | Day-Month-Year

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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

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b) Hardness

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c) Elasticity

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d) Stiffness

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e) Toughness

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f) Stress

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g) Strain

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h) Yield strength

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i) Modulus of elasticity

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j) Modulus of rigidity

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k) Creep

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l) Resilience

______


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(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: ___

Quenched: ___

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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(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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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)


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(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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Manufacturing process change: ___

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Give definitions for the following (1 mark each)

a) Dendritic Structure

______

b) BCC

____________

c) FCC

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d) Allotropy

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e) Recrystallisation

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f) Amorphous

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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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(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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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 6.02mmPoint A B C D E F G H J

Load (kN) 0 19.8 0 24.8 0.5 27.6 27.3Elong (m) 0 188 9 298 9 756 894

(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)___________________________________


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(c) Calculate the UTS. (1 mark)______________________________________________

(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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(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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(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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(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.

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D.


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REFERENCE SECTION

Alkane Formula Boiling point [°C] Melting point [°C]

Density [g·cm3] (at 20 °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

Tin / lead phase diagram


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