Posted: May 20th, 2015

# ASSIGNMENT 2

ASSIGNMENT 2

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

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