Xinyi Minnie Liu
Examiner: Wole Soboyejo, Dan Steingart
Advisor: Craig Arnold
Wole started first.
1.
Draw me a simple cubic and you apply a uniaxial force on it, what is the stiffness? What is the difference between stiffness and Young’s modulus
(stiffness has unit of N/m).
2.
Draw me the interatomic potential curve. How do you determine modulus from the diagram, is it bulk modulus or young’s modulus?
3.
Derive the theoretical strength.
4.
Draw me a crystal with an edge dislocation in it. Derive an equation for shear strain. (Gamma=xb/L). What is dislocation density? Relate dislocation density to the shear strain. Write an equation for shear strain rate. What do you think this equation tells you.
5.
Then we talked about dislocations. Why a polycrystalline material has a higher strength than a single crystal material? I said grain boundaries.
Dislocations pile up at the grain boundaries. He asked me whether dislocations can move across grain boundaries. He asked me to draw a bicrystal structure and asked me what is in common at the interface. (The strain is the same at the interface)
6.
Why crack will propagate? I derived the Griffith equation and talked about fracture toughness. (He asked me to distinguish between toughness and fracture toughness). Then he ask me if I saw G=K^2/E, what is G and what is the relationship between G and K(it is in MSE501 notes, Fracture Chapter)
Dan asked about characterization skills.
1.
SEM. What is SEM? How does it work( draw the SEM diagram)? Describe about SEM(SE and BSE mode)? What can you tell from the BSE mode and why? I said BSE gives us compositional information, but it is actually information about elements. So then I said we have to use XRD to identify the phases. Then we start to talk about XRD.
2.
XRD: What is XRD? How does it work? What does the background noise look like? What about for amorphous material? What about for gas? (For gas and amorphous material, you will get some diffraction even at a small angle).
What other information can you obtain from XRD? How do you relate the diffraction angle with diffraction pattern? How does X-rays be generated?
(Know the difference between X-rays in XRD and characteristic X-rays used in EDS)
Then he said sometimes instead of changing the angle, you change the wavelength(lamda). What is the benefit of doing that? (I said something and he said we will get back to this)
3.
TEM. Describe about TEM. (three modes) What does a diffraction pattern look like? I said X-rays diffraction can be thought as one dimension of the
Debye circle, and he asked me how to relate those. Then we started to talk about why instead of changing the angle, you change the wavelength.

Summary:
Both Dan and Wole are very nice and give you hints and help you walk through the problem when you get stuck. Dan focuses on characterization techniques and Wole focuses on the Mechanics class that he taught.
Besides 505 classnotes, I find this website to be very helpful: http://www.ammrf.org.au/myscope/sem/practice/
Good luck!