Piazza questions

Question 1

What is the equation for plastic strain?

Answer 1

Plastic strain = total strain - (stress/elastic modulus)

Question 2

What are the four types of metal structure?

Answer 2

Simple cubic, hexagonal close-packed, face-centred cubic, body-centred cubic

Question 3

What type of brackets does a plane vector have?

Answer 3

(101)

Question 4

What type of brackets does a direction vector have?

Answer 4

[012]

Question 5

What are advantages of the Charpy and Izod testing techniques?

Answer 5

Simplicity
Ease of specimen manufacture
Small amount of analysis required
Large material databases
People are familiar with the method

Question 6

What are disadvantages of the Charpy and Izod testing techniques?

Answer 6

Sensitive to minor changes in specimen dimensions and positioning
Different machines can give different results
Modest changes in surface condition or temp. result in big changes to impact toughness
Underlying physics is unclear

Question 7

What is a material’s mechanical loss coefficient?

Answer 7

A measure of its capacity to absorb mechanical energy. Low = high energy transfer efficiency, high = great vibration damper

Question 8

What is wear resistance?

Answer 8

A material’s resistance to repetitive contacts

Question 9

What is fatigue strength?

Answer 9

Resistance to failure by cyclic loading

Question 10

What is cleavage?

Answer 10

Separation of atomic planes due to applied force

Question 11

What constitutes a slip system?

Answer 11

The combination of a slip plane and direction

Question 12

What is the equation for shear stress on a given slip plane?

Answer 12

s.s. = stress*Cos(phi

Question 13

What is the equation for shear stress on a given slip plane?

Answer 13

s.s. = stressCos(phi)Cos(psi), where phi is the angle between the slip plane and the cross-sectional plane, and psi is the angled between the applied force and the slip direction.

Question 14

What is the Schmid factor? What is its maximum possible value? Why?

Answer 14

S factor = Cos(phi)Cos(psi) in the shear strain equation

Maximum = 0.5 - at this point the applied stress needed to cause plastic deformation is at a minimum

Question 15

What’s the equation for calculating cos(phi) and cos(psi) in the shear stress equation, given that the slip system is (abc)[123] and the applied stress is in the [xyz] direction??

Answer 15

cos(phi) = (ax + by + cz)/(sqrt(x^2 + y^2 + z^2) + sqrt(a^2 + b^2 + c^2))

cos(psi) = (1x + 2y + 3z)/(sqrt(1^2 + 2^2 + 3^2) + sqrt(x^2 + y^2 + z^2))

Question 16

What’s the equation for calculating cos(phi) and cos(psi) in the shear stress equation, given that the slip system is (abc)[123] and the applied stress is in the [xyz] direction??

Answer 16

cos(phi) = (ax + by + cz)/(sqrt(x^2 + y^2 + z^2) + sqrt(a^2 + b^2 + c^2))

cos(psi) = (1x + 2y + 3z)/(sqrt(1^2 + 2^2 + 3^2) + sqrt(x^2 + y^2 + z^2))

Question 17

What is brittle-ductile transition?

Answer 17

BCC metals such as steel have temperature-dependent critical shear stresses - at lower temperatures this means their toughness may drop suddenly

Question 18

How do strengthening effects stack?

Answer 18

Additively

Question 19

What happens to the rate of strengthening as more and more alloying is introduced to a material?

Answer 19

The strengthening effect diminishes - strength is proportional to the square root of concentration

Question 20

What is grain size strengthening? How is it achieved?

Answer 20

Decreasing the grain size in a polycrystal so as to increase the length of the grain boundaries.