question

elastic means _____
plastic means _____

answer

elastic means REVERSIBLE
plastic means PERMANENT

question

common states of stress:
- simple tension
- torsion
- simple compression
- bi-axial tension
- hydrostatic compression

match: pressurized tank, balanced rocks, cable, fish under water, drive shaft

answer

common states of stress:
- simple tension - CABLE
- torsion - DRIVE SHAFT
- simple compression - BALANCED ROCKS
- bi-axial tension - PRESSURIZED TANK
- hydrostatic compression - FISH UNDER WATER

question

units of stress

answer

units of stress:
N/m^2
lb/in^2

question

units of strain

answer

units of strain:
NONE

question

what is hooke's law?

answer

? = ? ?

? = stress
? = modulus of elasticity (young's modulus)
? = strain

question

Slope of stress strain plot (which is proportional to the elastic modulus) depends on what property?

answer

Slope of stress strain plot (which is proportional to the elastic modulus) depends on what property?
BOND STRENGTH
Steeper the slope, stronger the bond

question

What is yield strength?

answer

yield strength: ?y, stress at which noticeable plastic deformation has occurred

question

what is tensile strength?

answer

tensile strength: TS, MAXIMUM STRESS ON ENGINEERING STRESS-STRAIN CURVE
metals - occurs when noticeable necking starts
polymers - occurs when polymer backbone chains are aligned and about to break

question

what is ductility? how can we measure it?

answer

ductility is PLASTIC TENSILE STRAIN at FAILURE.
measure it by %EL or %RA

question

what is toughness?

answer

toughness is the ENERGY to BREAK a unit volume of material. approximate by the area under the stress-strain curve

question

What is hardness?

answer

hardness is RESISTANCE TO PERMANENTLY INDENTING THE SURFACE.
large hardness means:
- resistance to plastic deformation or cracking in compression.
- better wear properties

question

2 ways to measure hardness

answer

hardness measurement:
ROCKWELL
HB = BRINELL HARDNESS

question

Why do "true" stress and strain exist?

answer

Cross sectional area changes when sample is stretched

question

Stress measures _____
Strain measures _____

answer

Stress measures LOAD
Strain measures DISPLACEMENT
(both size independent measures)

question

What is hardening?

answer

Hardening is an INCREASE in YIELD STRENGTH
due to PLASTIC DEFORMATION.

question

Elastic modulus is a _____ property.

answer

Elastic modulus is MATERIAL property

• Critical properties depend largely on sample flaws (defects,
etc.). Large sample to sample variability.

question

Describe dislocation motion in metals.

answer

• Metals (Cu, Al):
Dislocation motion EASIEST
- non-directional bonding
- close-packed directions
for slip

question

Describe dislocation motion in covalent ceramics.

answer

• COVALENT Ceramics (Si, diamond)
Motion DIFFICULT
- directional (angular) bonding

question

Describe dislocation motion in ionic ceramics.

answer

• Ionic Ceramics (NaCl):
Motion DIFFICULT
- need to avoid nearest
neighbors of like sign (- and +)

question

Metals - plastic deformation occurs by ____ – an edge
dislocation (extra half-plane of atoms) slides over adjacent
plane half-planes of atoms.

answer

Metals - plastic deformation occurs by SLIP – an edge
dislocation (extra half-plane of atoms) slides over adjacent
plane half-planes of atoms.

question

If dislocations ___ ____, plastic deformation doesn't occur!

answer

If dislocations CAN'T MOVE, plastic deformation doesn't occur!

question

A dislocation moves along a slip plane in a slip direction
______ to the dislocation line
• The slip direction is the same as the _____ vector direction

answer

A dislocation moves along a slip plane in a slip direction
PERPENDICULAR to the dislocation line (This is on his notes but would anyone like to explain that to me)
• The slip direction is the same as the BURGERS vector direction

question

Slip System

– Slip plane - plane on which ______ slippage occurs
• Highest _____ densities (and large interplanar spacings)

– Slip directions - directions of _____ movement
• Highest _____ densities

answer

Slip System

– Slip plane - plane on which EASIEST slippage occurs
• Highest PLANAR densities (and large interplanar spacings)

– Slip directions - directions of DISLOCATION movement
• Highest LINEAR densities

question

What is meant by resolved shear stress? ?_R

answer

What is meant by resolved shear stress? ?_R

results from applied tensile stresses -- factors in the angles between the applied stress and the slip direction & slip plane normal

Condition for dislocation motion: ?_R> ?_{CRSS (Critcally resolved shear stress)}

?_R= ?*cos?*cos?

?_Rmaximum at ? = ? = 45 degrees
__________________________________________

? = applied tensile stress = F/A
? = angle between F and slip direction (Fs)
? = angle between F and slip plane normal (As)

question

For deformation to occur the _____ stress must
be greater than or equal to the ______ stress

answer

For deformation to occur the APPLIED stress must
be greater than or equal to the YIELD stress

question

SLIP MOTION in POLYCRYSTALS

• Polycrystals stronger than single crystals – ____ _____ are barriers to dislocation motion.

• Slip planes & directions (?, ?) change from one grain to another.

• ____will vary from one grain to another.

• The grain with the ______ ?_R yields first. • Other (less favorably oriented) grains yield later.

answer

SLIP MOTION in POLYCRYSTALS

• Polycrystals stronger than single crystals – GRAIN BOUNDARIES are barriers to dislocation motion.

• Slip planes & directions (?, ?) change from one grain to another.

• ?_R will vary from one grain to another.

• The grain with the LARGEST ?_R yields first. • Other (less favorably oriented) grains yield later.

question

Four Strategies for Strengthening:

answer

Four Strategies for Strengthening:
1: Reduce Grain Size
2: Form Solid Solutions
3: Precipitation Strengthening
4: Cold Work (Strain Hardening)

question

Why would we want to Reduce Grain Size

answer

1. Reduce Grain Size
- A strategy for STRENGTHENING
- Grain boundaries are barriers to slip.
- Barrier "strength“ increases with increasing angle of misorientation.
- Smaller grain size: more barriers to slip.

question

Why would we want to Form Solid Solutions

answer

2: Form Solid Solutions
- strategy for STRENGTHENING
- IMPURITY ATOMS DISTORT the lattice & generate lattice STRAINS.
- These strains can act as barriers to dislocation motion.

question

- Small impurities tend to concentrate at dislocations in regions of _____ strains
- Large impurities tend to concentrate at dislocations in regions of _____ strains.
- both ____ mobility of dislocations and ____ strength

answer

- Small impurities tend to concentrate at dislocations in regions of COMPRESSIVE strains
- Large impurities tend to concentrate at dislocations in regions of TENSILE strains.
- both REDUCE mobility of dislocations and INCREASE strength

question

Alloying increases _____ strength and _____ strength

answer

Alloying increases YIELD strength and TENSILE strength

question

Why is Precipitation Strengthening useful

answer

Precipitation Strengthening:

Hard precipitates are difficult to shear.
Ex: Ceramics in metals (SiC in Iron or Aluminum).
basically means it just cuts thru the precipitate

Either shears them or bows out around them

question

What are the 4 common forming operations that reduce the cross sectional area during Cold Work (Strain Hardening)

answer

• Cold worDeformation at room temperature (for most metals).
• Common forming operations reduce the cross-sectional area:
- forging
- rolling
- drawing
- extrusion

%CW = Ao-Ad/Ao x 100

question

How does the dislocation structure change during cold working?

answer

Dislocations entangle with one another during cold work.
• Dislocation motion becomes more difficult.

question

What happens to
- yield strength
- tensile strength
- ductility
as cold work is INCREASED

answer

as COLD WORK is INCREASED:

- YIELD STRENGTH (?y) INCREASES.
- TENSILE STRENGTH (TS) INCREASES.
- DUCTILITY (%EL or %AR) DECREASES.

can check values by looking at graph

question

Effect of heat treating after cold work?

answer

Heat treating after cold work...
• 1 hour treatment at Tanneal...
decreases TS and increases %EL.
• Effects of cold work are nullified!

question

What are the 3 annealing stages?

answer

3 Annealing stages:
1. Recovery
2. Recrystallization
3. Grain growth

question

The 1st step of annealing, RECOVERY, does what?

answer

RECOVERY REDUCES the number of DISLOCATIONS

question

The 2nd step of annealing, RECRYSTALLIZATION, does what?

answer

RECRYSTALLIZATION forms new grains that:
- have LOW dislocation densities
- are SMALL in size
- consume and replace parent cold-worked grains

question

The 3rd step of annealing, GRAIN GROWTH, does what?

answer

GRAIN GROWTH:

at longer times, average grain size increases
- small grains shrink and ultimately disappear
- large grains continue to grow

question

T_R = RECRYSTALLIZATION TEMPERATURE = temperature at which recrystallization just reaches completion in ___.

0.3T_m < T_R < 0.6T_m

For a specific metal/alloy, T_R depends on:
• %CW -- T_R DECREASES with _____ %CW
• Purity of metal -- T_R DECREASES with _____ purity

answer

T_R = RECRYSTALLIZATION TEMPERATURE = temperature at which recrystallization just reaches completion in 1 HOUR.

0.3T_m < T_R < 0.6T_m

For a specific metal/alloy, T_R depends on:
• %CW -- T_R DECREASES with INCREASING %CW
• Purity of metal -- T_R DECREASES with INCREASING purity

question

STRENGTHENING IN METALS SUMMARY:

• Dislocations are observed primarily in ____ and _____.
• Strength is _____ by making dislocation motion difficult.
• Strength of metals may be increased by:
-- ______ grain size
-- solid _____ strengthening
-- _______ hardening
-- ____ working
• A cold-worked metal that is ____ treated may experience
recovery, recrystallization, and grain growth – its properties
will be altered.

answer

STRENGTHENING IN METALS SUMMARY:

• Dislocations are observed primarily in METALS and ALLOYS.
• Strength is INCREASED by making dislocation motion difficult.
• Strength of metals may be increased by:
-- DECREASING grain size
-- solid SOLUTION strengthening
-- PRECIPITATE hardening
-- COLD working
• A cold-worked metal that is HEAT treated may experience
recovery, recrystallization, and grain growth – its properties
will be altered.

question

Ductile fracture
– Accompanied by significant _____ deformation

Brittle fracture
– Little or no _____ deformation
– Catastrophic

answer

Ductile fracture
– Accompanied by significant PLASTIC deformation

Brittle fracture
– Little or no PLASTIC deformation
– Catastrophic

question

Ductile vs Brittle Failure (picture it)

answer

[image]

question

Ductile fracture is usually ____ desirable than brittle fracture

answer

Ductile fracture is usually MORE desirable than brittle fracture

question

• Ductile failure:
-- [one/many] piece(s)
-- [small/large] deformation(s)

• Brittle failure:
-- [one/many] piece(s)
-- [small/large] deformation(s)

answer

• Ductile failure:
-- ONE piece
-- LARGE deformation

• Brittle failure:
-- MANY pieces
-- SMALL deformations

question

Brittle fracture surfaces:

1. ______ (between grains)
2. ______ (through grains)

answer

Brittle fracture surfaces:

1. INTERGRANULAR (between grains)
2. TRANSGRANULAR (through grains)

question

Moderately ductile failure stages

answer

[image]

question

TS engineering materials [>>/<<] TS perfect materials

answer

TS engineering materials << TS perfect materials

question

DaVinci (500 yrs ago!) observed...
-- the longer the wire, the smaller the load for failure.
• Reasons:
--
--

answer

DaVinci (500 yrs ago!) observed...
-- the longer the wire, the smaller the load for failure.
• Reasons:
-- FLAWS CAUSE PREMATURE FAILURE
-- larger samples contain longer flaws!

question

_____ are stress concentrators!

answer

FLAWS are stress concentrators!

question

Cracks having [sharp/blunt] tips propagate easier than cracks having [sharp/blunt] tips

[Brittle/ductile] materials have sharp crack tips
[Brittle/ductile] materials have blunt crack tips

answer

Cracks having SHARP tips propagate EASIER than cracks having BLUNT tips

BRITTLE materials have sharp crack tips
DUCTILE materials have blunt crack tips

question

Energy balance on the crack:
- ______ _____ energy-
• Energy stored in material as it is elastically deformed.
• This energy is released when the crack propagates.
• Creation of new surfaces requires energy

answer

Energy balance on the crack:
- ELASTIC STRAIN energy-
• Energy stored in material as it is elastically deformed.
• This energy is released when the crack propagates.
• Creation of new surfaces requires energy

question

what will cause a crack to propagate?

answer

Crack propagates if crack-tip stress (?m) EXCEEDS a critical stress (?c)

the critical stress is that equation with a = half length of internal crack & specific surface energy & modulus of elasticity

question

How do we find out how much energy goes into failing a material? (Hint: A mechanical way of measuring toughness)

answer

Impact Testing

1 example is charpy testing (actually kinda neat, maybe watch the online lecture, idk if its important tho)

- severe testing case
- makes material more brittle
- decreases toughness

question

Toughness can change depending on ductile-to-brittle transition temperature (DBTT)

answer

Toughness can change depending on ductile-to-brittle transition temperature

there is a graph on the powerpoint

Higher temp = more ductile

Design strategy: stay above the DBTT (so things dont get brittle and break)

question

Fatigue = failure under applied ____ stress.

Stress varies with ____.

• Key points: Fatigue...
--can cause part failure, even though ?max < ?y.
--responsible for ~ 90% of mechanical engineering failures.

answer

Fatigue = failure under applied CYCLIC stress.

Stress varies with TIME.

• Key points: Fatigue...
--can cause part failure, even though ?max < ?y.
--responsible for ~ 90% of mechanical engineering failures.

question

Types of fatigue behavior:

S = STRESS AMPLITUDE

- Fatigue limit, Sfat:
--no fatigue if S [] Sfat

- For some materials, there is no fatigue limit! (Al)

answer

Types of fatigue behavior:

S = STRESS AMPLITUDE

- Fatigue limit, Sfat:
--no fatigue if S < Sfat

- For some materials, there is no fatigue limit! (Al)

question

Cracks grow incrementally:

-- crack grows faster as
• change in stress [increases/decreases]
• _____ gets longer
• loading freq. [decreases/increases].

answer

Cracks grow incrementally:

-- crack grows faster as
• change in stress INCREASES
• CRACK gets longer
• loading freq. INCREASES.

question

Improving fatigue life:

1.

2.

answer

Improving fatigue life:

1. Impose compressive surface stresses (to SUPPRESS SURFACE CRACKS FROM GROWING)

2. Remove stress concentrators (AVOID SHARP EDGES)

question

Primary Creep: slope (creep rate) _____ with time.

Secondary Creep: steady-state
i.e., constant slope (??/?t).

Tertiary Creep: slope (creep rate)
_____ with time, i.e. _____ of rate.

answer

Primary Creep: slope (creep rate) DECREASES with time.

Secondary Creep: steady-state
i.e., constant slope (??/?t).

Tertiary Creep: slope (creep rate)
INCREASES with time, i.e. ACCELERATION of rate.

question

Creep is temperature dependent

Occurs at elevated temperature, T > ___ Tm (in K)

answer

Creep is temperature dependent

Occurs at elevated temperature, T > 0.4 Tm (in K)

question

Secondary Creep:

Strain rate is _____ at a given T, ?

strain rate increases with _____ T, ?

answer

Secondary Creep:

Strain rate is CONSTANT at a given T, ?

strain rate increases with INCREASING T, ?

question

SUMMARY OF MATERIAL FAILURES:

• Sharp corners produce ____ stress concentrations
and premature failure.

• Engineering materials [as strong / not as strong] as predicted by theory

• Flaws act as stress concentrators that cause failure at
stresses lower than _____ values.

• Failure type depends on T and s :

-For simple fracture (noncyclic s and T < 0.4Tm), failure stress decreases with:
- ____ maximum flaw size,
- ____ T,
- ____ rate of loading.

- For _____ (cyclic s):
- cycles to fail decreases as Ds increases.

- For _____ (T > 0.4Tm):
- time to rupture decreases as s or T increases.

answer

SUMMARY OF MATERIAL FAILURES:

• Sharp corners produce LARGE stress concentrations
and premature failure.

• Engineering materials NOT AS STRONG as predicted by theory

• Flaws act as stress concentrators that cause failure at
stresses lower than THEORETICAL values.

• Failure type depends on T and s :
-For simple fracture (noncyclic s and T < 0.4Tm), failure stress
decreases with:
- INCREASED maximum flaw size,
- DECREASED T,
- INCREASED rate of loading.
(logical^)

- For FATIGUE (cyclic s):
- cycles to fail decreases as Ds increases.

- For CREEP (T > 0.4Tm):
- time to rupture decreases as s or T increases.

question

Ceramics:
compounds of ____ and _____ elements

answer

Ceramics:
compounds of METALLIC and NON-METALLIC elements

e.g. Al2O3, ZrO2, MgO, TiO2, SiC, WC, B4C, ZnS, TiB2 and carbon…

question

_______ ceramics:
- china, porcelain, bricks, tiles, glasses
- many based on clays

______ ceramics - oxides, carbides, nitrides
- used in electronics, computers, aerospace…

answer

TRADITIONAL ceramics:
- china, porcelain, bricks, tiles, glasses
- many based on clays

TECHNICAL ceramics - oxides, carbides, nitrides
- used in electronics, computers, aerospace…

question

Ceramic Structure/Composition:
• At least __ elements - sometimes more (BaTiO3, Ti3, SiC2)
? [more/less] complex structures than metals
• Determined by bonding:
- ranges from ~purely ____ to ~purely ____
- many exhibit combination of both

answer

Ceramic Structure/Composition:
• At least 2 elements - sometimes more (BaTiO3, Ti3, SiC2)
? MORE complex structures than metals
• Determined by bonding:
- ranges from ~purely IONIC to ~purely COVALENT
- many exhibit combination of both

question

Ceramic bonding:
-- Mostly _____ with varying degrees of ____.
-- % ionic character increases with difference in
_____ of atoms.

answer

Ceramic bonding:
-- Mostly IONIC with varying degrees of COVALENCY.
-- % ionic character increases with difference in
ELECTRONEGATIVITY of atoms.

question

(Ceramics) If Predominantly Ionic:

• Consider as electrically charged ____, not ____
• Positively charged ____ ions (cations), e.g. Ca2+
– Given up valence e to _____ anions
– Generally _____ than anions

• Negatively charged ______ ions (anions),e.g. F
– Accepted valence e from _____ cations
– Generally _____ than cations

answer

(Ceramics) If Predominantly Ionic:

• Consider as electrically charged IONS, not ATOMS

• Positively charged METALLIC ions (cations), e.g. Ca2+
– Given up valence e to NON-METALLIC anions
– Generally SMALLER than anions

• Negatively charged NON-METALLIC ions (anions),e.g. F
– Accepted valence e from METALLIC cations
– Generally LARGER than cations

question

Key factors influencing ceramic structure:
1.
2.

answer

Key factors influencing ceramic structure:
1. Magnitude of electrical charges
- crystal must be ELECTRICALLY NEUTRAL
- required charge balance dictates ratio of # cations to anions
2. Relative sizes (IONIC RADII) of cations to anions
- each cation prefers max # nearest neighbor anions and vise versa, this determines how ions pack in crystal

question

Non-metallic anions (-) much ____ than metallic cations (+)
• Pack like atoms in metals

______ metallic cations may thus fit into the spaces (i.e. the
_____ sites)

answer

Non-metallic anions (-) much LARGER than metallic cations (+)
• Pack like atoms in metals

SMALLER metallic cations may thus fit into the spaces (i.e. the INTERSTITIAL sites)

question

What are the two possible types of ceramic interstitial sites? Give some info on both.

answer

Tetrahedral Sites: 4 anion spheres as nearest neighbors
• 3 in 1 plane + 1 in adjacent plane surround site
• CN = 4
• rcation/ranion -> .225 - .414

Octahedral Sites: 6 anion spheres as nearest neighbors
• 3 each, in 2 planes
• CN = 6
• rcation/ranion -> .414 - .732

question

What determines which site the cations will occupy?

answer

What determines which site the cations will occupy?

1. Size of sites:
– does the cation fit in the site?

2. Stoichiometry:
– if all of one type of site is full, the remainder have to go into other types of sites

3. Bond Hybridization:
– % covalency

question

What determines which site the cations will occupy?

1. Size: Must form stable structures:
• ____ the # of oppositely charged ion neighbors.
• CN related to cation-anion radius ratio, CN ____ with increasing rcation/ranion

answer

What determines which site the cations will occupy?

1. Size: Must form stable structures:
• MAXIMIZE the # of oppositely charged ion neighbors.
• CN related to cation-anion radius ratio, CN INCREASES with increasing rcation/ranion

question

Crystal structure stoichiometry:

If, for a specific ceramic, each unit cell has 6 cations and these prefer the (octahedral) OH sites, then:
– __ will go into (octahedral) OH
– __ will go into (tetrahedral) TD

answer

Crystal structure stoichiometry:

If, for a specific ceramic, each unit cell has 6 cations and these prefer the (octahedral) OH sites, then:
– 4 will go into (octahedral) OH
– 2 will go into (tetrahedral) TD

question

List the AX-Type crystal structures

AX-Type means EQUAL # of cations and anions

answer

List the AX-Type crystal structures:

1. NaCl (ROCK SALT)
2. CsCl (Cesium Chloride)

question

Describe NaCl (ROCK SALT) structure:

- can be considered as 2 interpenetrating ___ lattices: one of cations and one of anions
- CN = __
- cations prefer ____ sites

answer

1. NaCl (ROCK SALT)
- can be considered as 2 interpenetrating FCC lattices: one of cations and one of anions
- CN = 6
- cations prefer OCTAHEDRAL sites

question

Describe CsCl (Cesium Chloride) structure:

- Each ion has __ neighbors
- ___ sites preferred
- like a ___ but not ___ since there are two different kind of ions.

answer

Describe CsCl (Cesium Chloride) structure

- Each ion has 8 neighbors
- CUBIC sites preferred
- like a BCC but not BCC since there are two different kind of ions.

question

Describe Zinc Blende (ZnS) structure:

- small Zn cations sit between __ S anions, CN = __
- Happens when .225<rc/ra<.0414
- Zn is in the ____ interstitial site
- __ of the possible ______ sites are occupied
- The bonding is usually highly ______

answer

Describe Zinc Blende (ZnS) structure:

- small Zn cations sit between 4 S anions, CN = 4
- Happens when .225<rc/ra<.0414
- Zn is in the TETRAHEDRAL interstitial site
- 4 of the possible TETRAHEDRAL sites are occupied
- The bonding is usually highly COVALENT (ZnS, ZnTe, SiC).

question

AmXp - Type Crystal Structures

Charges on cations and anions are not equal (m and/or p ? 1)

• Calcium Fluorite (CaF2)

• rc/ra ~ 0.8, CN = __

• Cations in ____ sites

• Similar to ____ but only half of cubic sites are occupied

• Unit cells consist of 8 “sub-cubes”
- e.g. UO2, ThO2, ZrO2, CeO2

• ______ structure – positions of cations and anions reversed
- e.g. Li2O, Na2O

answer

AmXp - Type Crystal Structures

Charges on cations and anions are not equal (m and/or p ? 1)

• Calcium Fluorite (CaF2)

• rc/ra ~ 0.8, CN = 8

• Cations in CUBIC sites

• Similar to CsCl but only half of cubic sites are occupied

• Unit cells consist of 8 “sub-cubes”
- e.g. UO2, ThO2, ZrO2, CeO2

• ANTIFLUORITE structure – positions of cations and anions reversed
- e.g. Li2O, Na2O

question

AmBnXp Crystal Structures

• >1 type of ___
• ____ structure

• Ex: complex oxide BaTiO3
• ____ crystal structure
• Ba2+ cations at corners
• Ti4+ cation in center
• O2- anions at each face
center

answer

AmBnXp Crystal Structures

• >1 type of CATION
• PEROVSKITE structure

• Ex: complex oxide BaTiO3
• CUBIC crystal structure
• Ba2+ cations at corners
• Ti4+ cation in center
• O2- anions at each face
center

question

Diamond (Similar to ___ ___)

- A _____ form of carbon

– ____ bonding of carbon
• hardest material known
• very ___ thermal conductivity

– Large single crystals – gem stones
– Small crystals – used to grind/cut other materials
– Diamond thin films
• hard surface coatings – used for cutting tools, medical devices, etc.

answer

Diamond (Similar to ZINC BLENDE)

- A POLYMORPHIC form of carbon

– TETRAHEDRAL bonding of carbon
• hardest material known
• very HIGH thermal conductivity

– Large single crystals – gem stones
– Small crystals – used to grind/cut other materials
– Diamond thin films
• hard surface coatings – used for cutting tools, medical devices, etc.

question

______:

- A POLYMORPHIC form of carbon
– Layered structure – parallel hexagonal arrays of carbon
atoms
-- Weak Van der Waal’s forces between layers
– Planes slide easily over one another -- good lubricant

answer

GRAPHITE:

- A POLYMORPHIC form of carbon
– Layered structure – parallel hexagonal arrays of carbon
atoms
-- Weak Van der Waal’s forces between layers
– Planes slide easily over one another -- good lubricant

question

2 more polymorphic forms of carbon:

• _____ – spherical cluster of 60 carbon atoms, C60
– Like a soccer ball
• _____ – sheet of graphite rolled into a tube
– Ends capped with fullerene hemispheres

answer

2 more polymorphic forms of carbon:

• FULLERENES – spherical cluster of 60 carbon atoms, C60
– Like a soccer ball
• CARBON NANOTUBES – sheet of graphite rolled into a tube
– Ends capped with fullerene hemispheres

question

Point defects in ceramics:

• _____ exist in ceramics for both cations and anions
• ______ exist for cations, but are not normally observed for anions because anions are large relative to the _____ sites

answer

Point defects in ceramics:

• VACANCIES exist in ceramics for both cations and anions
• INTERSTITIALS exist for cations, but are not normally observed for anions because anions are large relative to the INTERSTITIAL sites (not saying its impossible, just far less likely)

question

• ____ Defect
-- a paired set of cation and anion vacancies.
• ____ Defect
-- a cation vacancy-cation interstitial pair.

answer

• SHOTTKY Defect
-- a paired set of cation and anion vacancies.
• FRENKEL Defect
-- a cation vacancy-cation interstitial pair.

question

_________ must be maintained when impurities are present

answer

ELECTRONEUTRALITY (charge balance) must be maintained
when impurities are present

When there is a SUBSTITUTIONAL cation or anion, the substitution must have equal charge to what is being taken away (so if 2 Na+ is replaced with 1 Ca2+, there will be a substitutional cation and a cation vacancy)

question

Diffusion of ____ is more complicated than in ____ due to the motion of two ionic species with opposite charges.

• Diffusion usually occurs by a ___ mechanism.
• Local charge neutrality must be maintained, so diffusion of an ion must be accompanied by the diffusion of an ion(s) with equal and opposite charge.
• Therefore diffusion is rate limited by the ____ moving ion.

answer

Diffusion of CERAMICS is more complicated than in METALS due to the motion of two ionic species with opposite charges.

• Diffusion usually occurs by a VACANCY mechanism.
• Local charge neutrality must be maintained, so diffusion of an ion must be accompanied by the diffusion of an ion(s) with equal and opposite charge.
• Therefore diffusion is rate limited by the SLOWER moving ion.

question

Ceramic materials are ____ brittle than metals: Why is this
so?

• Consider mechanism of deformation:
– In crystalline, by ____ motion
– In highly ionic solids, ___ motion is difficult
• few slip systems
• resistance to motion of ions of like charge (e.g., anions) past one another

answer

Ceramic materials are MORE brittle than metals: Why is this
so?

• Consider mechanism of deformation:
– In crystalline, by DISLOCATION motion
– In highly ionic solids, DISLOCATION motion is difficult
• few slip systems
• resistance to motion of ions of like charge (e.g., anions) past one another

question

In general, why do ceramics fail?

answer

In general, ceramics fail due to BRITTLE FRACTURE before any plastic deformation occurs.

• Cracks propagate either transgranularly or intergranularly.

• Initiation sites are from small flaws that are present in the material which serve as stress risers.

• Because there is no mechanisms for plastic deformation, crack blunting cannot occur, leading to cracks propagating un-impeded above a certain stress.

Sometimes cracks can propagate slowly at stresses lower that
defined by the equation above (Kic = Y(delta)(sqrt(pi*a)) in moist environments leading to stress corrosion process at the crack tip.

question

Chalk cut from bulk material shows how different pieces could have different flaws.
• This leads to a statistical variation in the tensile strength.
• This distribution of cracks also creates a ____ dependence on strength since more cracks would be in a larger sample.
• A brittle rod will be stronger in ___ than in ____.

answer

Chalk cut from bulk material shows how different pieces could have different flaws.
• This leads to a statistical variation in the tensile strength.
• This distribution of cracks also creates a VOLUME dependence on strength since more cracks would be in a larger sample.
• A brittle rod will be stronger in BENDING than in TENSION. (tension is applied to the entire sample and cracks propagate in tension... with bending there is tension at some points, compression in others, so the tension is being applied to a smaller amount of the sample, making it less likely to have these flaws.

question

____ _____ Ps(Vo) is the fraction of identical samples, with volume Vo which survive loading to a tensile stress, (Delta)

who can you thank for this

answer

SURVIVAL PROBABILITY Ps(Vo) is the fraction of identical samples, with volume Vo which survive loading to a tensile stress, (Delta)

as stress increases, Survival probability decreases

THANKS WEIBULL

question

Modulus of rupture, DELTAr is larger than tensile strength for two reasons:

answer

Modulus of rupture, DELTAr is larger than tensile strength for two reasons:
• In bending half the beam is subjected to compression leading
to flaws closing up.
• The peak tensile stress is below the center load with stress
lower in other areas leading to a small volume being
subjected to high tensile stress.

question

Give 3 examples of applications for ceramics

answer

Give 3 examples of applications for ceramics
1. DIE BLANKS
2. CUTTING TOOLS
3. SENSORS

question

What are refractories?

answer

Refractories are materials to be used at HIGH TEMPERATURES.

question

Materials for Automobile engines:

Advantages:
– Operate at high temperatures – high efficiencies
– Low frictional losses
– Operate without a cooling system
– Lower weights than current engines

Disadvantages:
– Ceramic materials are brittle
– Difficult to remove internal voids (that weaken structures)
– Ceramic parts are difficult to form and machine

• Potential candidate materials: Si3N4, SiC, & ZrO2
• Possible engine parts: engine block & piston coatings

answer

Probably wont ask this directly as a question?, but it has important observations about applying ceramics:

Materials for Automobile engines:

Advantages:
– Operate at high temperatures – high efficiencies
– Low frictional losses
– Operate without a cooling system
– Lower weights than current engines

Disadvantages:
– Ceramic materials are brittle
– Difficult to remove internal voids (that weaken structures)
– Ceramic parts are difficult to form and machine

• Potential candidate materials: Si3N4, SiC, & ZrO2
• Possible engine parts: engine block & piston coatings

question

SUMMARY OF CERAMICS:

• Interatomic bonding in ceramics is ____ and/or ____.
• Ceramic crystal structures are based on:
-- maintaining ____ ____
-- cation-anion ____ ___ .
• Imperfections
-- Atomic point: vacancy, interstitial (cation), Frenkel, Schottky
-- Impurities: substitutional, interstitial
-- Maintenance of charge neutrality
• Room-temperature mechanical behavior – flexural tests
-- ____-____; measurement of elastic modulus
-- brittle fracture; measurement of ____ ____

answer

SUMMARY OF CERAMICS:

• Interatomic bonding in ceramics is IONIC and/or COVALENT.
• Ceramic crystal structures are based on:
-- maintaining CHARGE NEUTRALITY
-- cation-anion RADII RATIOS .
• Imperfections
-- Atomic point: vacancy, interstitial (cation), Frenkel, Schottky
-- Impurities: substitutional, interstitial
-- Maintenance of charge neutrality
• Room-temperature mechanical behavior – flexural tests
-- LINEAR-ELASTIC; measurement of elastic modulus
-- brittle fracture; measurement of FLEXURAL MODULUS.

question

what is a polymer?

answer

poly = many
mer = repeat unit

question

• Originally natural polymers were used
– Wood – Rubber
– Cotton – Wool
– Leather – Silk

• Oldest known uses
– Rubber balls used by Incas
– Woven cloth

answer

idk how to make this a question but its probably good to kno

• Originally natural polymers were used
– Wood – Rubber
– Cotton – Wool
– Leather – Silk

• Oldest known uses
– Rubber balls used by Incas
– Woven cloth

question

Polymers since WWII

• Most plastics, rubbers, fibers today are _____ polymers…
– Some of the first? ___ & ___
• Since WW II, synthetic polymers have revolutionized the
materials field:
– ____ to produce
– ____ can be controlled as desired
– Often superior to natural materials
– Supplanted metals & wood in some applications:
• lower cost & superior properties
• _____ concerns…recycling, resource usage &
conservation…sustainability

answer

Polymers since WWII

• Most plastics, rubbers, fibers today are SYNTHETIC polymers…
– Some of the first? BAKELITE & NYLON
• Since WW II, synthetic polymers have revolutionized the
materials field:
– CHEAP to produce
– PROPERTIES can be controlled as desired
– Often superior to natural materials
– Supplanted metals & wood in some applications:
• lower cost & superior properties
• ENVIRONMENTAL concerns…recycling, resource usage &
conservation…sustainability

question

Most polymers are ______
– i.e., made up of H and C

answer

Most polymers are HYDROCARBONS
– i.e., made up of H and C

question

Polymer composition:

• Strong covalent _____-molecular bonds
– 4 valence e- per C atom
– 1 valence e- per H atom
– Recall CH4…4 x single covalent bonds…

• Weaker hydrogen and van der Waals ____molecular
bonds:
– Thus polymers have ____ melting/boiling points

answer

Polymer composition:

• STRONG covalent INTRA-molecular bonds
– 4 valence e- per C atom
– 1 valence e- per H atom
– Recall CH4…4 x single covalent bonds…

• WEAKER hydrogen and van der Waals INTERmolecular
bonds:
– Thus polymers have LOW melting/boiling points

question

Saturated hydrocarbons
– Each carbon singly bonded to ___ other atoms.
– All covalent bonds are ____ bonds.
– Example:
• Ethane, C2H6
– No new atoms can be joined without removal of others already bonded.

answer

Saturated hydrocarbons
– Each carbon singly bonded to FOUR other atoms.
– All covalent bonds are SINGLE bonds.
– Example:
• Ethane, C2H6
– No new atoms can be joined without removal of others already bonded.

question

Unsaturated Hydrocarbons
• Share _ or _ pairs of electrons.
• Double & triple bonds somewhat _____ – can form new bonds
• Each carbon not bonded to 4 other atoms
– Other atoms or groups can bond to the original
molecule

answer

Unsaturated Hydrocarbons
• Share 2 or 3 pairs of electrons.
• Double & triple bonds somewhat UNSTABLE – can form new bonds
• Each carbon not bonded to 4 other atoms
– Other atoms or groups can bond to the original
molecule

Double bond found in ethylene or ethene - C2H4
Triple bond found in acetylene or ethyne - C2H2

question

Polymer molecules are very large – _____
– ____ bonds within each molecule
– Backbone = string of __ atoms singly bonded to each other
– Remaining 2 valence electrons are used for side-bonds to atoms and radicals
– ex. Ethylene (C2H4) is a gas at room temp but can be a polymer building block

answer

Polymer molecules are very large – MACROMOLECULES
– COVALENT bonds within each molecule
– Backbone = string of C, CARBON atoms singly bonded to each other
– Remaining 2 valence electrons are used for side-bonds to atoms and radicals
– ex. Ethylene (C2H4) is a gas at room temp but can be a polymer building block

question

Chemistries other than pure HC are possible:
– Polymerize (CF2=CF2) --> PTFE (Teflon®)
– Fluorocarbons
– PVC which is similar to ethylene where 1 in 4 H replaced
with Cl

General forumla:

-CH2-CHR-

R = ____ or _____

answer

Chemistries other than pure HC are possible:
– Polymerize (CF2=CF2) --> PTFE (Teflon®)
– Fluorocarbons
– PVC which is similar to ethylene where 1 in 4 H replaced
with Cl

General forumla:

-CH2-CHR-

R = ATOMS or GROUPS

question

Chain Repeat Units
– If all the same: _____
– If different: _____

answer

Chain Repeat Units
– If all the same: HOMOPOLYMERS
– If different: COPOLYMERS

question

_______ polymerization

– Monomer unit daisy-chained 1 at a time to form linear
macromolecule
– 3 stages: initiation, propagation & termination

- Chain forms via sequential addition of monomer units
– Active site (unpaired e-) transfers to each successive end
monomer

• Termination:
– Active ends of 2 propagating chains may link: ____
– Dead chains are possible, e.g. via H atom: _____

answer

FREE RADICAL polymerization

– Monomer unit daisy-chained 1 at a time to form linear
macromolecule
– 3 stages: initiation, propagation & termination

- Chain forms via sequential addition of monomer units
– Active site (unpaired e-) transfers to each successive end
monomer

• Termination:
– Active ends of 2 propagating chains may link: COMBINATION
– Dead chains are possible, e.g. via H atom:
DISPROPORTIATION

question

________ polymerization

– Intermolecular reactions involving >1 monomer species giving off a low MW condensate (e.g. H2O)
– E.g. Nylon 6,6

answer

CONDENSATION polymerization

– Intermolecular reactions involving >1 monomer species giving off a low MW condensate (e.g. H2O)
– E.g. Nylon 6,6

question

______ ______ Polymer (3-D Crosslinking)
– Phenol-Formaldehyde (Phenolic)

answer

THERMOSET NETWORKED Polymer (3-D Crosslinking)
– Phenol-Formaldehyde (Phenolic)

question

Describe Isomerism

answer

ISOMERISM:
– Two compounds with same chemical formula can have quite different structures

ex. C8H18 can be normal octane or 2,4-dimethylhexane

question

Thermoplastics vs. Thermosets

answer

THERMOPLASTICS
• Linear polymers with 2 links/mer
• They can be softened (and melted) repeatedly by raising the temperature.
• Weak secondary bonds between chains.
• Strong bonds within chains.

THERMOSETS
• Crosslinked with 3 links/mer
• Rigid 3-D molecules
• After a thermoset is formed, it CANNOT be reshaped or remelted.

question

Not all chains in a polymer are of the same ____
— i.e., there is a distribution of molecular weights

answer

Not all chains in a polymer are of the same LENGTH
— i.e., there is a distribution of molecular weights

question

• MW can be defined in several ways:
• Number averaged,

answer

DP = average number of repeat units per chain

question

Molecular Shape (or _______):
– Chain bending and twisting are possible by ____ of carbon atoms around their chain single bonds
– note: not necessary to ____ chain bonds to alter molecular shape

answer

Molecular Shape (or CONFORMATION):
– Chain bending and twisting are possible by ROTATION of carbon atoms around their chain single bonds
– note: not necessary to BREAK chain bonds to alter molecular shape

question

Chain ________ = r

r << total chain length

Large # of chains:
• Each may bend, coil or kink
• Extensive chain entanglement
• Governs some mechanical properties,
e.g. in elastomers

answer

Chain END-TO-END DISTANCE = r

r << total chain length

Large # of chains:
• Each may bend, coil or kink
• Extensive chain entanglement
• Governs some mechanical properties,
e.g. in elastomers

question

Physical characteristics of polymers depend on:
1.
2.
3.

answer

Physical characteristics of polymers depend on:
1. MOLECULAR WEIGHT
2. SHAPE
3. STRUCTURE

question

List the 4 covalent chain configurations in order of increased strength

answer

[image]

question

• Linear polymer:

? Repeat units joined end-to-end
? Long flexible chains (“spaghetti”)
? Extensive _____ and ____ bonds betweenchains
? PE, PVC, PS, MPPA, Nylon, fluorocarbons

answer

• Linear polymer:

? Repeat units joined end-to-end
? Long flexible chains (“spaghetti”)
? Extensive VAN DER WAALS and HYDROGEN bonds between chains
? PE, PVC, PS, MPPA, Nylon, fluorocarbons

question

Branched polymer:

• Side-branch chains connected to main chain
• Chain packing efficiency ____
• ____ density
• LDPE

answer

Branched:

• Side-branch chains connected to main chain
• Chain packing efficiency REDUCED
• LOWER density
• LDPE

question

• Crosslinked polymer:

? Adjacent chains joined by ____ bonds
? Occurs during ____
? Non-reversible
? Rubbers (via vulcanization using S atoms)

answer

• Crosslinked polymer:

? Adjacent chains joined by COVALENT bonds
? Occurs during SYNTHESIS
? Non-reversible
? Rubbers (via vulcanization using S atoms)

question

Network polymer:

• Monomers forming __ or more covalent bonds
• Form 3-D networks
• Epoxies, polyurethanes, phenol-formaldehyde

answer

Network polymer:

• Monomers forming 3 or more covalent bonds
• Form 3-D networks
• Epoxies, polyurethanes, phenol-formaldehyde

question

______ are mirror images – can’t superimpose without breaking a bond

answer

STEREOISOMERS are mirror images – can’t superimpose without breaking a bond

question

Configurations – to change must ____ ____

answer

Configurations – to change must BRAEAK BONDS

question

______ – stereoregularity or spatial arrangement of R units along chain
_____ – all R groups on same side of chain
_____ – R groups alternate sides
_____ – R groups randomly positioned

answer

TACTICITY – stereoregularity or spatial arrangement of R units along chain
ISOTACTIC – all R groups on same side of chain
SYNDIOTACTIC – R groups alternate sides
ATACTIC – R groups randomly positioned

question

Geometrical isomerism within repeat units with ____
bonds between chain C atoms:

- cis: H atom and CH3 group on the same side of the chain
- trans: H atom and CH3 group on opposite sides of the chain

Isomers have the same or different properties?
Can you convert from cis to trans?

answer

Geometrical isomerism within repeat units with DOUBLE
bonds between chain C atoms:

- cis: H atom and CH3 group on the same side of the chain
- trans: H atom and CH3 group on opposite sides of the chain

Isomers have the same or different properties? DIFFERENT
Can you convert from cis to trans? NO

question

What are 4 possible arrangements for copolymers (two or more monomers polymerized together)

answer

question

Crystallinity in Polymers:

• Involves _____ as opposed to atoms in metals & ceramics
• More complex atomic arrangements
• Crystallinity due to packing of polymer chains to generate an
ordered atomic array.
• Complex ____ ____
• Chain twisting, coiling & kinking all promote disorder:
? Disorder = amorphous regions
? Most polymers thus only partially crystalline
? Combination of ____ + ____ regions
• Range from 100% amorphous to ~95% crystalline
• Density = fn.(% crystallinity)

answer

Crystallinity in Polymers:

• Involves MOLECULES as opposed to atoms in metals & ceramics
• More complex atomic arrangements
• Crystallinity due to packing of polymer chains to generate an
ordered atomic array.
• Complex UNIT CELLS
• Chain twisting, coiling & kinking all promote disorder:
? Disorder = amorphous regions
? Most polymers thus only partially crystalline
? Combination of CRYSTALLINE + AMORPHOUS regions
• Range from 100% amorphous to ~95% crystalline
• Density = fn.(% crystallinity)

question

How does an increase in % crystallinity of a polymer affect:
TS and E

How does heat treating affect % crystallinity?

answer

How does an increase in % crystallinity of a polymer affect:
TS (INCREASE)
and E (INCREASE)

How does heat treating affect % crystallinity? It causes crystalline regions to grow and % crystallinity to INCREASE

question

Single polymer crystals – only for ____ and carefully ____ growth rates

answer

Single polymer crystals – only for SLOW and carefully CONTROLLED growth rates

question

Some semicrystalline polymers form spherulite structures
• Alternating chain-folded crystallites and amorphous regions
• Spherulite structure for relatively ___ growth rates
- has a ______ site at the center

answer

Some semicrystalline polymers form SPHERULITE structures
• Alternating chain-folded crystallites and amorphous regions
• Spherulite structure for relatively RAPID growth rates
- has a NUCLEATION site at the center

question

Strengths of polymers ~__% of those for metals

answer

Strengths of polymers ~10% of those for metals

question

Picture the deformation of BRITTLE crosslinked and network polymers

answer

[image]

question

Picture the deformation of SEMICRYSTALLINE (PLASTIC) polymers

answer

[image]

question

Picture the deformation of ELASTOMERS

answer

[image]

question

What does the stress strain curve look like for BRITTLE polymers, PLASTIC polymers, and ELASTOMERS

answer

[image]

question

Influence of T on Thermoplastics:

Decreasing T...

-- ____ E
-- ____ TS
-- ____ %EL

answer

Influence of T on Thermoplastics:

Decreasing T...

-- INCREASES E
-- INCREASES TS
-- DECREASES %EL

question

Influence of strain rate on Thermoplastics:

Increases strain rate...

-- ____ E
-- ____ TS
-- ____ %EL

answer

Influence of strain rate on Thermoplastics:

Increases strain rate...

-- INCREASES E
-- INCREASES TS
-- DECREASES %EL

question

What is Tm and Tg?

answer

Tm = MELTING TEMP
Tg = GLASS TRANSITION TEMP

question

What factors affect Tm and Tg?

answer

What factors affect Tm and Tg?

Both Tm and Tg increase with increasing chain stiffness

• Chain stiffness increased by presence of
1. Bulky sidegroups
2. Polar groups or sidegroups
3. Chain double bonds and aromatic chain groups

• Regularity of repeat unit arrangements – affects Tm only

question

How can we increase chain stiffness, in turn increasing Tm and Tg?

answer

Chain stiffness increased by presence of

1. Bulky sidegroups
2. Polar groups or sidegroups
3. Chain double bonds and aromatic chain groups

question

Regularity of repeat unit arrangements – affects [Tm/Tg] only

answer

Regularity of repeat unit arrangements – affects Tm only

question

Craze formation prior to cracking:
– during crazing, plastic deformation of spherulites
– and formation of ____ and ____ bridges

answer

Craze formation prior to cracking:
– during crazing, plastic deformation of spherulites
– and formation of MICROVOIDS and FIBRILLAR bridges

question

Processing of Polymers:

_______
– Can be reversibly cooled & reheated, i.e. recycled
– Heat until soft, shape as desired, then cool
– Examples: polyethylene, polypropylene, polystyrene.

________
– When heated forms a molecular network
(chemical reaction)
– Degrades (doesn’t melt) when heated
– Prepolymer molded into desired shape, then
chemical reaction occurs
– Examples: urethane, epoxy

answer

Processing of Polymers:

THERMOPLASTIC
– Can be reversibly cooled & reheated, i.e. recycled
– Heat until soft, shape as desired, then cool
– Examples: polyethylene, polypropylene, polystyrene.

THERMOSET
– When heated forms a molecular network
(chemical reaction)
– Degrades (doesn’t melt) when heated
– Prepolymer molded into desired shape, then
chemical reaction occurs
– Examples: urethane, epoxy

question

List 4 methods of processing polymers and which type (thermoplastic or thermoset) it applies to

answer

List 4 methods of processing polymers and which type (thermoplastic or thermoset) it applies to:

1. COMPRESSION MOLDING
thermoplastics and thermosets

2. INJECTION MOLDING
thermoplastics and some thermosets

3. EXTRUSION
thermoplastics
BLOWN-FILM EXTRUSION for plastic bags*** we watched a video on this, might actually be important

question

polymer fibers are formed by _____.

- extrude polymer through a spinneret (a die containing many small orifices)
– the spun fibers are drawn under tension
– leads to highly aligned chains
- fibrillar structure

primary use in textiles

answer

polymer fibers are formed by SPINNING.

- extrude polymer through a spinneret (a die containing many small orifices)
– the spun fibers are drawn under tension
– leads to highly aligned chains
- fibrillar structure

primary use in textiles

question

polymer fiber characteristics

answer

polymer fiber characteristics
1. high tensile strengths
2. high degrees of crystallinity
3. structures containing polar groups

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