Mechanical Metallurgy

1. Draw stress strain curve for ductile metal. Mark points of interest. Why does the slope of the curve change

2. Draw the curve for mild steel. Why are there two yield points? Why do these occur?

3. Why does the slope change after necking? Why does load decrease?

4. What is the condition for necking to take place? What is this condition called?

5. Why does strain hardening occur?

6. Is it correct to say that the material deforms only plastically after the yield point? What is the difference between non-linear and plastic deformation?

7. What happens if the stress strain curve is plotted at different temperatures? How does the point of fracture differ in these cases?

8. Why do screw dislocations cross slip? What is the relation between stacking fault energy (SFE) and tendency to cross slip?

9. Why do dislocations break into partials? Do partials exist in pairs or can exist independently?

10. Why slip occurs only on closely packed planes?

11. What is precipitation hardening?

12. Why is martensite brittle?

13. How do you determine the direction of burgers vector when the direction of Extra Half Plane and dislocation line are given?

14. Do like dislocations always repel? Why do dislocations attract or repel?

15. How do dislocations interact with other defects? With point defects? With precipitates?

16. How do dislocations interact with each other? (all possible cases and outcomes)

17. What are jogs and kinks?

18. Why dislocations form loops? Why can’t dislocations end within a crystal?

19. What are the limitations of Hall-Petch relations? Derive Hall-Petch relation.

20. What is inverse Hall-Petch relation?

21. What is Bauschinger Effect?

22. What is yielding? What are commonly used Yield criteria? If you were to define a new criteria how would you decide if it is valid?

23. Does stress cause strain or does strain cause stress? Give examples.

24. Are dislocations equilibrium defects?

25. What is the difference between Peierls-Nabarro stresses and CRSS?

26. What are the sources of dislocations? Can dislocations be created using thermal energy alone like vacancies?

27. What is a Cottrell atmosphere?

28. How does dislocation interlocking occur in FCC?

29. What is Thomson tetrahedron?

30. What are tilt and twist boundaries?

31. Why does more cold work lead to higher dislocation density?

32. If Stress as well as Pressure both mathematically are given by force per unit area, why is one a tensor and other a scalar?

33. When invariants are considered, why does the model use first invariant of stress tensor and second and third invariants of deviatoric stress tensor?

34. What are the characteristic behaviour of viscoelastic materials? (Effect of strain rate on stress and time dependence at constant stress)

35. Derive relationships between true and engineering stresses

36. Why do we say that the true stress strain curve lies upwards and to the left of the engineering stress strain curve? How do the relations change before and after necking?

37. Why does the portion of the sample apart from the neck undergo relaxation?

38. Transformation requires the product of two sines and/or two cosines. What does this mean?

39. Why is the stress tensor symmetrical along the diagonal? What makes it so?

40. How can the stress relations for Mohr circle be derived? What is the maximum and minimum principal stress?

41. How is a similar calculation carried out for strains? What are the assumptions?

42. What are the boundary conditions used in mechanics to make simple assumptions for solutions?

Footnotes