Lecture 03/24

Question 1

What is slip?

Answer 1

Process by which plastic deformation is produced by dislocation motion

Question 2

What is a slip plane?

Answer 2

Crystallographic plane along which the dislocation line travels

Question 3

Where are dislocations introduced?

Answer 3

During solidification, plastic deformation, consequence of thermal stress that result from rapid cooling?

Question 4

How can we define density?

Answer 4

Total dislocation length per unit vol or number of dislocations per unit area

Question 5

When metals are plastically deformed, 5% of what is retained internally?

Answer 5

Strain energy

Question 6

Why does lattice distortion exist?

Answer 6

Extra half-plane of atoms

Question 7

Lattice strains are imposed on?

Answer 7

Neighboring atoms

Question 8

What is a slip system?

Answer 8

Slip plane and slip direction

Question 9

The slip plane will be along?

Answer 9

The greatest planar density

Question 10

Slip direction will be in the direction of?

Answer 10

Highest linear density

Question 11

What is the difference between elastic and plastic deformation?

Answer 11

• Elastic is nonpermanent, temporarily stretching interatomic bonds
• Plastic interatomic bonds are ruptured

Question 12

What are the 2 fundamental dislocation types?

Answer 12

Edge and screw

Question 13

Describe an edge dislocation

Answer 13

Localized lattice distortion response to a shear stress applied perpendicular to it’s line

Question 14

Dislocation motion is analagous to?

Answer 14

Caterpillar motion

Question 15

For a screw dislocation, the dislocation line is?

Answer 15

Perpendicular to the stress direction

Question 16

What is attractive force?

Answer 16

Dislocations of opposite sign and some slip plane

Question 17

What is resolved shear stress?

Answer 17

Shear stress component when slip plane oriented is neither perpendicular nor parallel to the direction of stress

Question 18

What are the two types of plastic deformation?

Answer 18

Slip and twinning

Question 19

What are the three mechanisms for strengthening metals?

Answer 19

• Grain size reduction
• Solid solution strengthening
• Strain hardening

Question 20

The atomic disorder within a grain boundary results in?

Answer 20

Discontinuity of slip planes

Question 21

What is solid solution strengthening?

Answer 21

Alloying with impurity atoms that go into either substitutional or interstitial solid solution

Question 22

What is strain hardening?

Answer 22

Cold working resulting in reduction in cross sectional area

Question 23

Explain strain-hardening

Answer 23

Dislocation density increases with cold working, the distance between dislocations decreases, dislocation motion is hindered

Question 24

Restoration of plastically deformed specimens results from?

Answer 24

Recovery and recrystallization

Question 25

How does recovery work?

Answer 25

Internal strain energy is relieved by virtue of dislocation motion, reduction in dislocations, electrical and thermal conductivities recover to their pre-cowrked states

Question 26

How does recrystallization work?

Answer 26

Formation of new strain-free grains that have low dislocation densities, are small, and consume and replace parent grains

Question 27

What happens if strain-free grains are left at an elevated temperature?

Answer 27

Grain size increases, small grains shrink, large grains continue to grow

Question 28

Strength is increased by?

Answer 28

Decreasing dislocation mobility