Microstructure and performance

Question 1

What is the incompressibility condition?

Answer 1

Plastic deformation occurs without a change in volume, plasticity depends on shear independent of pressure

Question 2

What is the effective stress?

Answer 2

A multiaxial measure of shear

Question 3

What are principle stress/strain?

Answer 3

Normal to orthogonal planes on which there are no shears

Question 4

What is an edge dislocation?

Answer 4

Burgers perpendicular to dislocation line

Question 5

What is a screw dislocation?

Answer 5

Burgers parallel to dislocation line (screw goes in parallel to screwdriver)

Question 6

Compare the stored energy of the types of dislocations

Answer 6

Stored energy for edge is higher than that of screw but both are proportional to the burgers vector squared

Question 7

Where is slip likely to occur?

Answer 7

In the farthest separated (a large), most densely packed (b small) planes in close-packed directions

Question 8

What are microcantilever beams used for?

Answer 8

To identify the activated slip systems and their critically resolved shear stress

Question 9

What is a constraint and what is its effect?

Answer 9

Can be a gb or hydrostatic stress state

It leads to a rotation of the lattice in order to shear

Question 10

What is the deformation vector composed of?

Answer 10

The undeformed vector and the displacement vector

Question 11

What is the deformation matrix?

Answer 11

3x3 that maps the undeformed material to its deformed configuration

Question 12

What are the components of the deformation tensor in 2D?

Answer 12

symmetric part - strain

asymmetric part - rotation

Question 13

What are the Cauchy Green tensors?

Answer 13

Measures deformation
C - with respect to the undeformed configuration
B - with respect to the deformed configuration

Question 14

What are the almanac strain tensor and the true strain tensor with respect to?

Answer 14

the deformed configuration

Question 15

What is the green strain tensor with respect to?

Answer 15

the undeformed configuration

Question 16

What is the polar decomposition theorem?

Answer 16

Any arbitrary deformation can always be multiplicatively decomposed into a rigid body rotation and stretch

Question 17

What are the properties of the rotation tensor?

Answer 17

R - Orthogonal

Question 18

What is the property of the stretch tensor?

Answer 18

Symmetric

Question 19

What is the shear strain?

Answer 19

The relative displacement of two slip planes with unit distance separation

Question 20

For single crystal what are the components of shear?

Answer 20

Symmetric - plastic strain

Asymmetric - rotation

Question 21

What is the Peierls energy?

Answer 21

The energy to move dislocation

Question 22

What determines the glide velocity?

Answer 22

Local thermal activation

Question 23

What is the total dislocation density?

Answer 23

The sum of sessile and glissile dislocations (SSDs and GNDs)

Question 24

What are SSDs?

Answer 24

Statistically stored dislocations are sessile and contribute to no net open burgers circuit, proportional to plastic strain accumulation

Question 25

What are GNDs?

Answer 25

Geometrically necessary dislocations are glissile and give lattices curvature and net open burgers circuit

Question 26

What is the length scale effect?

Answer 26

Smaller samples under strain gradient experience greater plastic strain hardening

Question 27

Which circumstances does the length scale effect occur?

Answer 27

Presence of particles
Polycrystal deformation
Two-phase alloys

Question 28

What is the strain rate sensitivity of alloys dependent on?

Answer 28

The activation volume

Question 29

What is EBSD?

Answer 29

Electron back scatter diffraction

Question 30

What are the main components of EBSD?

Answer 30

SEM column, control
Computer
Output
Camera

Question 31

What is the convention of euler angles?

Answer 31

1 - rotation about z axis
0 - rotation about new x axis
2 - rotation about new z axis