Material Science Part 2

Front 1

engineering stress =?

Back 1

force/surface area

Front 2

engineering strain = ?

Back 2

(l-l0)/l0

change in length/ original length

Front 3

E (young's modulus) = ?

Back 3

stress/strain

Front 4

T or F: elastic deformation is reversible.

Back 4

True

Front 5

Poisson's ratio (v) =?

Back 5

v = -width strain/ axial strain

Front 6

Yield strength (sigma y) =?

Back 6

- point at which plastic deformation occurs

-if nonlinear draw line from strain=0.2%

-if noisy take average of max and min

Front 7

At plastic deformation?

Back 7

- irreversible deformation occurs

- bonds are broken and formed

- can only recover up to elastic deformation

Front 8

Resilience (Ur) =?

Back 8

ability to absorb energy by elastic deformation

(up to yield stress)

Ur = 1/2 * ((sigma y) ^2)/E

Front 9

Strength def.

Back 9

how much force a sample can withstand without failure

Front 10

factor of safety (N) =?

Back 10

yield stress/applied stress

(assume 2 if none given)

Front 11

Toughness (Ut)= ?

Back 11

Ability to absorb energy up to fracture

Ut = integral from 0 to strain at fracture of sigma dstrain

Front 12

Ultimate tensile stress (UTS) =?

Back 12

- highest point of stress before fracture

- point at which necking begins

Front 13

Ductility def.

Back 13

degree of plasic deformation before fracture

Front 14

dislocation under shear stress =?

Back 14

movement of dislocations along slip plane direction

Front 15

critical resolved shear stress=?

Back 15

minimum required to produce slip

tau R = sigma y/2

Front 16

Hardness =?

Back 16

surface resistance to plastic deformation

Front 17

To strengthen materials (and hinder motion of dislocations) we can use:

Back 17

- cold working

- solid solution strengthening

- precipitation hardening

- grain size reduction

Front 18

cold working = ?

Back 18

plastically deforming the material at low temps

(increases dislocation density)

%CW = (A0 -Ad)/A0 *100

Ad = surface area after dislocation

Front 19

Solid solution strengthening = ?

Back 19

adding impurities/ alloying to rrestrict dislocation movement (strains on surrounding atoms)

Front 20

Why does grain size reduction increase hardness?

Back 20

the movements of dislocations stop at grain boundaries

Front 21

before necking:

strain=?

stress=?

Back 21

strain = ln( 1+ engineering strain)

stress = engineering stress(1+ engineering strain)

Front 22

After necking:

strain = ?

stress= ?

Back 22

strain = ln (SA/SAi)

stress= engineering stress(SA/SAi)

SAi = instantaneous surface area

Front 23

constant electrical field, force= ?

Back 23

F = q * E

q = charge

E = electrical field

Front 24

Ohms law:

Back 24

velocity = mu * E

mu = (tau*|q|)/mass

j = sigma*E

Front 25

current density (j)=?

Back 25

j = n|q|v

n = # of particles

v = velocity

Front 26

conductivity (sigma) =?

Back 26

sigma = n|q|mu

sigma = 1/resistivity

Front 27

nucleation = ?

Back 27

creation of nuclei that happens at critical radius

Front 28

What is the difference between homogenous and heterogeneous nucleation?

Back 28

homogeneous = probability of forming nuclei is the same everywhere

heterogeneous = more probable at the mould walls

Front 29

As melting temperature increases>> critical nucleus?

Back 29

decreases

and number of nuclei increases

Front 30

growth stage of solidification = ?

Back 30

growth of nuclei (if radius is larger than the critical)

- occurs in opposite direction of heat flow

- forms dendrites

Front 31

as cooling rate increases >> number of nuclei?

Back 31

increases

Front 32

as cooling rate increases >> dendrite size?

Back 32

decreases

Front 33

as cooling rate increases >> mechanical properties?

Back 33

increase

Front 34

annealing and recrystallization are used for?

Back 34

softening material to recover workability

Front 35

What are the three stages of annealing?

Back 35

recovery, recrystallization, grain growth

Front 36

during recovery what happens?

Back 36

- reduce defects

- reordering of atoms

Front 37

during recrystallization what happens?

Back 37

- form new grains

Front 38

during grain growth what happens?

Back 38

grain size increases

(mechanical properties decrease)

Front 39

What are ceramics?

Back 39

inorganic compounds of metals and nonmetals

Front 40

What is the fluorite structure?

Back 40

Ca in FCC

F in tetrahedral sites

ex: UO2, ThO2

Front 41

What is the anti-fluorite structure?

Back 41

O in FCC

Li in tetrahedral

ex: Li2O, M+Na2O

Front 42

What is the perovskite structure?

Back 42

FCCish

Ca in corners

O in face centers

Ti in 1/4 octahedral (1 in center)

ex: SrTiO3, BaTiO3

Front 43

What is the corundum structure?

Back 43

O in HCP

Al in 2/3 of octahedral

ex: Cr2O3, Fe2O3

Front 44

Which structure is diamond most like?

Back 44

zincblende

Front 45

What causes coarse pearlite?

Back 45

slower cooling

Front 46

bainite = ?

Back 46

ferrite and cementite

Front 47

martensite is obtained by?

Back 47

Quenching (rapid cooling) of austensite

(harder than bainite, pearlite, austenite etc)

Front 48

graph of heat treatments:

Back 48

Front 49

critical cooling rate = ?

Back 49

the minimum rate at which all is transformed into martensite

Front 50

What is a polymer?

Back 50

an organic compound made of repetitive units called monomers bonded via C-C covalent bonds

Front 51

Molecular weight of a polymer (Mn)=?

Back 51

Mn = M0*Xn

M0 = mol. weight of monomer

Xn = degree of polymerization

Front 52

Number raverage molecular weight = ?

Back 52

Mn = sum (Mi* ni)

Mi = weight of chain

ni = fraction with that weight

Front 53

What are the three types of polymer structures?

Back 53

linear, branched, cross-linked (network)

Front 54

What is tacticity and what are the three kinds?

Back 54

tacticity is the orientation of pendant groups

three types:

- isotactic = same side

- syndiotactic = alternating

- atactic = random

Front 55

Crystallinity = ?

Back 55

x = (rho c * (rho s - rho a)) / (rho s * (rho c - rho a))

rho c = density of crystalline regions

rho a = density of amorphous

rho s = density of sample

Front 56

Overall, what structural factors are better for crystallinity?

Back 56

Simpler! (chemical structure, molecular structure, isotactic, CIS (not TRANS), lower molecular rate)

Front 57

Higher polarization >> crystallinity?

Back 57

increases

Front 58

Cooling rate increases >> crystallinity

Back 58

decreases

Front 59

Molecular weight increases >> glass transition temperature?

Back 59

increases

Front 60

intermolecular interactions increase >> glass transition temperature?

Back 60

increases

Front 61

chain flexibility increases >> glass transition temperature?

Back 61

decreases

Front 62

more symmetric >> glass transition temperature?

Back 62

decreases

Front 63

polymer classification table:

Back 63