hes1230 s 1, 2012 exam paper.pdf

HES1230 of 16 Materials and Processes Semester 1, 2012

EXAMINATION DETAILS

Examination Cover Sheet SEMESTER 1 2012

Subject Code: HES1230 School: School of Engineering, Computing and Science

Subject Title: Materials and Processes

Duration: 120 min Reading time: 10min 50% of overall assessment covered by this exam CANDIDATE DETAILS Student to complete (do not use pencil) ID:

Surname: Given:

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outstanding fees and charges I am aware that I am not allowed to present for any special examination unless approval has been granted by the appropriate Swinburne or

external authority

STUDENT SIGNATURE: DATE:

INSTRUCTIONS TO CANDIDATES Material/equipment that is not on this list is unauthorised material. Where a student is found in possession of any unauthorised material:

1. That material will be removed as soon as it is detected; and 2. The Student Examination Irregularity procedures of the Assessment and Appeals Policy and

Procedures will be implemented. Materials Allowed: Students are NOT permitted to have any other material, including pencil cases, calculator cases, notes of any description, and any books.

Answering Instructions:

This paper contains 16 printed pages ( inclusive of cover sheet) Time allowed is two (2) hours and Ten(10) minutes of reading time

Answer ALL Questions

The marks for each question are as stated at the end of each question

All working must be done using pen

Pencil is only allowed for diagram

If you complete this exam before the set exam duration time, you may be asked to enter your time of departure. This information will have no bearing on your result.


Formula which may be useful in the Exam

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Section A Answer ALL Questions (25 Marks) Please write the answer in the table provided in answer sheet. 1. What is the predominant type of bonding for titanium (Ti)?

A. Ionic

B. Hydrogen

C. Covalent

D. van der Waals

E. Metallic

2. Which type(s) of bonds are found between atoms within hydrocarbon molecules?

A. Ionic bonds

B. Hydrogen bonds

C. Covalent bonds

D. van der Waals bonds

E. Metallic bonds

3. Which of the following materials may form crystalline solids?

A. Polymers

B. Metals

C. Ceramics

D. All of the above

4. For the face-centred cubic crystal structure: how many atoms are associated with each unit cell?

A. 4

B. 8

C. 12

D. 16


5. For the body-centered cubic crystal structure: what is the coordination number?

A. 4

B. 8

C. 12

D. 16

6. If the atomic radius R of a metal that has the face-centered cubic crystal structure is 0.137 nm, calculate the volume of its unit cell (in nm3). (Note: 1nm = 1 nano metre

= 1 x 10-9

metre) The unit cell for the face-centred cubic crystal structure is shown in the following sketch

7. The presence of a small amount of copper in aluminium significantly strengthens the alloy by:

A. Forming precipitates which hinder dislocation motion

B. Increasing its Young's Modulus

C. Binding atoms together, thus preventing slip

D. Rearrangement of the crystal structure resulting in fewer dislocations

8. The Planar density of the (111) plane of a Face Centred Cubic structure, whose unit

cell has a lattice parameter and atomic radius are given by a and R respectively, is

A. 26

3

R

B. 26

3

a

C. 6

3

D. None of the above

A. 0.0058 nm3

B. 0.5820 nm3

C. 5.8200 nm3

D. 0.0582 nm3


9. Toughness of materials is equal to area under _________ part of the stress-strain

curves.

A. Elastic

B. Plastic

C. Both A and B


10. Why is window glass transparent?

A. Because it has a single crystal structure and each sheet is cut with the optic axis normal to the plane of the window.

B. Because it has an amorphous structure with large interatomic spacing. Light waves can pass between widely spaced atoms without any interaction with the solid structure.

C. Because sheets of glass are cut thin enough for light to pass through without any significant absorption.

D. Because of the electronic nature of the bonds between the atoms in the glass.

11. Work hardening strengthens an alloy by:

A. Removing internal defects in the crystal structure

B. Increasing the dislocation density

C. Decreasing the grain size of the alloy

D. Increasing the lattice resistance to dislocation motion

12. Which one of the following is not associated with brittle failure?

A. Intergranular failure

B. Cleavage along crystallographic planes

C. Microvoid Coalescence

D. Crack propagation

13. A specimen of alloyed aluminium having a rectangular cross section 10.8 mm x 12.5 mm is pulled in tension with a force of 34,300 N, and produces only elastic deformation. Given that the elastic modulus of this metal is 79 GPa, calculate the resulting strain as closest in value to

A. 0.03220

B. 0.00233

C. 0.02320

D. 0.00322


14. The critical resolved shear stress for slip in a single crystal of pure zinc is 1.8 x 105 Pa. The magnitude of the tensile stress necessary to initiate slip when the angle between the tensile axis and slip direction is 30° and the angle between the tensile axis and the normal to the slip plane is 60° is calculated as

A. 0.42 MPa

B. 4.2 MPa

C. 42 MPa


15. The atoms surrounding an edge dislocation experience what kinds of strains?

A. Tensile strains

B. Shear strains

C. Compressive strains

D. Both A and C

16. For a bronze alloy, the stress at which plastic deformation begins is 267 MPa and the modulus of elasticity E is 115 GPa.

The maximum load (in N) that may be applied to a specimen having a cross-sectional area of 300 mm2 without plastic deformation is closest in value to:

A. 801 N

B. 8 010 N

C. 80 100 N

D. 80.1 N

17. Consider a brass alloy under a tensile test, the stress-strain behavior of which is shown below, a cylindrical specimen of this alloy having a length of 63 mm must elongate only 0.11 mm when a tensile load of 53,500 N is applied. Under these circumstances, the radius of the specimen is approximately (in mm):

A. 108 mm

B. 1.08 mm

C. 10.8 mm

D. 0.108 mm


18. During the recovery of a cold-worked material, the number of dislocations:

A. increase

B. decrease

C. interact

D. have no effect on the material

19. Oxidation of an atom involves the

A. loss of electrons

B. gain of electrons

C. loss of protons

D. gain of protons

20. Metals near the top of the galvanic series are

A. Cathodic

B. Anodic

C. Unreactive

D. Both A and C

21. A sacrificial anode in a corrosive environment is

A. when an inactive metal or alloy which does not corrode and nor protect another metal or alloy to which it is electrically coupled

B. when an inactive metal or alloy loses its chemical reactivity and becomes extremely inert

C. area reduction is used as a measure of ductility

D. when an active metal or alloy which preferentially corrodes and protects another metal or alloy to which it is electrically coupled

E. when different concentrations of ions or dissolved gases result in total dissolution

22. Which of the following describes crevice corrosion?

A. Corrosion that occurs preferentially along grain boundaries.

B. Corrosion resulting from the combined action of an applied tensile stress and a corrosive environment.

C. One element is preferentially removed as a result of corrosion.

D. Corrosion that results from a difference in concentration of ions or dissolved gases in the electrolyte.


23. The absorption of energy measured by an impact test would be expected to correlate with

A. hardness

B. the area under the stress-strain curve up to failure

C. tensile strength from a tensile test

D. failure stress from a tensile test

24. Semicrystalline thermoplastics differ from thermosets in that:

A. Thermoplastics have higher strength

B. Can be used as a matrix for composite materials

C. Can be in molten state

D. They demonstrate visco-elastic behaviour

25. Find the elastic modulus of fiber glass reinforced plastic in the longitudinal

direction if the modulus of elasticity of fibres is 65 GPa, matrix 2.5 GPa and volume fraction of fibres is 40%?

A. 27.5 GPa

B. 2.5 GPa

C. 65 GPa

D. 275 GPa


HES1230 Materials and Processes

Semester 1 2012, Final Exam

Answers for Section A

Student ID _________________________

Question Number Answer

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25


Section B

Answer ALL Questions (25 Marks)

B1 The Hall-Petch relationship, given by, 21

0

kdY shows the effects of changes in

grain sizes on the yield strength of the material.

i. What strengthening mechanism does this refer to and explain briefly the strengthening mechanism? [2]

ii. How do the changes in grain size affect the yield strength of a polycrystalline material? [2]


B2 The figure below (Figure B2 from Callister) shows the result of a creep test carried out at a constant load W and at temperature T C.

i. Label the deformation and stages of the creep in the diagram shown. [1]

ii. Sketch in the diagram, the expected creep curve if the testing temperature is being

increased to T1C (T1 > T) [2]

Answer

Figure B2


B3 A large sum of money is spent on corrosion prevention and maintenance as a resultant of corrosion reactions.

i. What are the two basic prerequisites for Galvanic Corrosion to take place?

[2]

ii. Give two measures or ways that can significantly reduce the effects of Galvanic Corrosion. [2]


B4 The diagram (Figure B4, from Callister) shows the S-N fatigue results for plain carbon steel (1045 steel), aluminium alloy (2014-T6) and red brass. Using the data given in the diagram, determine:

i. Fatigue or endurance limit of 1045 steel in terms of MPa. [1]

ii. What is the fatigue life for the 2014 –T6 aluminium alloy at an applied stress

amplitude of 150MPa [1]

iii. The Maximum stress Amplitude that can be applied to red brass in order to achieve a fatigue of 107 cycles. [1]

Figure B4


B5 A cylindrical rod 100 mm long and having a diameter of 10 mm is to be deformed using a

tensile load of 27,500 N. It must not experience either plastic deformation or a diameter reduction of more than 7.5 10-3 mm. Of the materials listed as follows, which are possible candidates? Justify your choice(s). [4]

Material Modulus of Elasticity

(GPa) Yield Strength

(MPa) Poisson’s Ratio

Aluminum alloy 70 200 0.33

Brass alloy 101 300 0.34

Steel alloy 207 400 0.30

Titanium alloy 107 650 0.34


B6 A continuous and aligned fiber-reinforced composite is to be produced consisting of 30

vol% aramid fibers and 70 vol% of a polycarbonate matrix. The modulus of elasticity of

aramid fiber is 131GPa and polycarbonate matrix is 2.4GPa. Assume that the composite

described has a cross-sectional area of 320 mm2 is subjected to a longitudinal load of

44,500 N.

(a) Calculate the fiber–matrix load ratio. [1]

(b) Calculate the actual loads carried by both fiber and matrix phases. [1]

(c) Compute the magnitude of the stress on each of the fiber and matrix phases. [2]

(d) What strain is experienced by the composite? [1]


B7 For the unit cells shown below, a, b and c have the same value equal to 1. Determine the Miller indices for the shaded planes shown in the follow diagrams (a) and (b)

[2]

END

(a) (b)

hes1230 s 1, 2012 exam paper.pdf

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