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Question 1

What is the peak strength of a bond?

Answer 1

The bond strength

Question 2

When is a bond “broken”?

Answer 2

When it is stretched more than ~10% of the original length. Strain~0.1

Question 3

What are the influential defects in strength?

Answer 3

Impurities (substitution and interstitial) Grain Boundaries Dislocations

Question 4

What is an Edge dislocation?

Answer 4

An extra “half a plane”

Question 5

What is a “dislocation line”?

Answer 5

Separates the part of the plane that has slipped from the part that has not

Question 6

How does a dislocation move?

Answer 6

Along a slip plane in a slip direction perpendicular to dislocation line

Question 7

What is a Screw dislocation?

Answer 7

Displacement parallel to the edge of the cut rather than perpendicular

Question 8

What is a Slip plane?

Answer 8

The plane on which easiest slip occurs (highest planar densities)

Question 9

What is Slip Direction?

Answer 9

Directions of movement (highest linear densities)

Question 10

When does slip occur?

Answer 10

Densely packed (Close packed) planes. Low energy is needed to slip

Question 11

Slip systems for FCC

Answer 11

Slip Plane- (111)

Slip Direction- (11_0)

No. of slip systems- 12

Question 12

Slip systems for BCC

Answer 12

Slip Planes- (110) (211) (321)

Slip Direction- All (1_11)

No.of slip systems- 12 12 24

Question 13

Slip systems for HCP

Answer 13

Slip Planes- (0001) (101_0) (101_1)

Slip Directions- All (112_0)

No. of slip systems- 3 3 6

Question 14

Resolved Shear Stress formula

Answer 14

tau_r=σ*cos(lambda)*cos(phi)

lambda=angle of slip plane

phi=angle of normal of slip plane

Question 15

Schmidt Factor, m=

Answer 15

cos(lambda)*cos(phi)

Question 16

When is resolved shear stress max?

Answer 16

lambda=phi=45º

Question 17

Why are HCP generally not as ductile as other metals?

Answer 17

There are less slip systmes that can be activated so slip is more difficult. Once slip can’t accomodate volume change, twinning occurs to compensate

Question 18

Why are ceramics brittle?

Answer 18

• Covalent ceramics- directional bonding
• Ionic ceramics- needs to avoid the nearest neighbours of like sign

Question 19

What are the 4 strategies for strengthening?

Answer 19

• Reduce grain size
• Form solid solutions
• Precipitation strengthening
• Cold working

Question 20

Why does reducing grain size increase strength?

Answer 20

Grain boundaries are barriers to slip. Strength of the barrier increases with increase of angle of misorientation

Smaller grains size- more barriers to slip

Question 21

Hall-Petch Equations, σ_yield=

Answer 21

σ₀+k_yd^-¼

Question 22

How does form solid solution increase strength?

Answer 22

Impurity atoms distort the lattie and generate lattice strains.

These can act as barriers to dislocation motion. Increasing critical resolved shear stress

Question 23

How does preciptaion strengthening increase strength?

Answer 23

Hard precipitates are difficult to shear. Large shear stress needed to move disloaction towards precipitate and shear it.

The dislocation “advances” but precipitates act as “pinning sites”

Question 24

How does cold woring increase strength?

Answer 24

Deformation at room temp. reduces x-sectional area.

Dislocations entangle with one another during cold working, dislocation mtion becomes more difficult

%CW = (A₀-A_d) *100/A₀

Question 25

3 Stages during Heat treatment

Answer 25

1. Recovery- Reduction of disloaction density by annihilation
2. Recrystalization- New grains form that; •have low dislocation densities, •small in size, •consume and replace parent cold-worked grains
3. Growth

Question 26

What happens to Tensile Strength 1 hour after Cold working?

Answer 26

TS decreases and Ductility (EL%) increase

Question 27

What is Isotropic?

Answer 27

Grains are equiaxed and randomly oriented