Engineering Materials.

This assignment is based on tutorials and answers should be supported by illustrations (sketches and graphs) wherever relevant. Any references used should be specified after each question.
All Answers must be less than or equal to ¾ of a page in 12 point Font, excluding graphics and references!
This second part of the tutorial assignment is due to be submitted by the end of the lecture in week 12.

7. Explain how you could obtain a minimum yield strength of 900MPa through the full thickness of a 100 mm diameter shaft manufactured from 4340 steel. This explanation should include specific details of the heat treatment processes and include temperatures/time and supporting data and graphs.
NOTE the diameter and steel grade (ie 4340) cannot be altered. (20 marks)

8. How would you differentiate between Surface Corrosion, pitting corrosion and crevice corrosion? (7 marks)

9. Would Iron (Fe) corrode in de-aerated dilute hydrochloric Acid (HCl)? (6 Marks)
Give the Equations and calculate the Gibbs Free Energy to determine your answer.

10. A steel tie rod 23 mm in diameter has the following minimum properties:
Yield Strength = 700MPa
Tensile Strength = 800Mpa
Fracture Toughness = 95MPam0.5

It was subjected to an axial tensile force of 300kN.
Determine its mechanical safety with respect to ductile and brittle fracture. Consider ß = 1.
Hint: Brittle fracture would occur if the rod contained a crack. (10 marks)

11. What would the following features on the fractured surface face of a broken shaft tell you about the mode of failure and the levels of stress that that shaft experienced? (7 marks)

(a) beach marks
(b) ratchet marks
(c) size of final fracture area

Engineering Materials
1, (a) A 10-mm-diameter Brinell hardness indenter produced an indentation 1.62 mm in diameter in a steel alloy when a load of 500 kg was used. Compute the HB of this material.
(b) What will be the diameter of an indentation to yield a hardness of 450 HB when a 500 kg load is used?

2. Cite five factors that lead to scatter in measured material properties.

3. A large tower is to be supported by a series of steel wires. It is estimated that the load on eachwire will be 11,100 N (2500 lbf). Determine the minimum required wire diameter assuming a factorof safety of 2 and a yield strength of 1030 MPa (150,000 psi).

4. (a) Compute the electrical conductivity of a 5.1-mm (0.2-in.) diameter cylindrical silicon specimen51 mm (2 in.) long in which a current of 0.1 A passes in an axial direction. A voltage of 12.5 V ismeasured across two probes that are separated by 38 mm (1.5 in.).
(b) Compute the resistance over the entire 51 mm (2 in.) of the specimen.

5. In a semiconductor, what charge carriers are present?

6. To what temperature would 25 lbm of a 1025 steel specimen at 25°C (77°F) be raised if 125 Btu ofheat is supplied?

7. A 0.1 m (3.9 in.) rod of a metal elongates 0.2 mm (0.0079 in.) on heating from 20 to 100°C (68 to212°F). Determine the value of the linear coefficient of thermal expansion for this material.
8. (a) Explain the two sources of magnetic moments for electrons.
(b) Do all electrons have a net magnetic moment? Why or why not?
(c) Do all atoms have a net magnetic moment? Why or why not?
9. Briefly explain why metals are opaque to electromagnetic radiation having photon energies withinthe visible region of the spectrum.

10. Can a material have an index of refraction less than unity? Why or why not?
11. Briefly explain what determines the characteristic color of (a) a metal and (b) a transparentnonmetal.