Term
elastic means _____
plastic means _____ |
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Definition
elastic means REVERSIBLE
plastic means PERMANENT |
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Term
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 |
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Definition
common states of stress:
- simple tension - CABLE
- torsion - DRIVE SHAFT
- simple compression - BALANCED ROCKS
- bi-axial tension - PRESSURIZED TANK
- hydrostatic compression - FISH UNDER WATER |
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Term
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Definition
units of stress:
N/m^2
lb/in^2 |
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Term
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Definition
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Term
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Definition
σ = Ε ε
σ = stress
Ε = modulus of elasticity (young's modulus)
ε = strain |
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Term
| Slope of stress strain plot (which is proportional to the elastic modulus) depends on what property? |
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Definition
Slope of stress strain plot (which is proportional to the elastic modulus) depends on what property?
BOND STRENGTH
Steeper the slope, stronger the bond
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Term
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Definition
| yield strength: σy, stress at which noticeable plastic deformation has occurred |
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Term
| what is tensile strength? |
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Definition
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 |
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Term
| what is ductility? how can we measure it? |
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Definition
ductility is PLASTIC TENSILE STRAIN at FAILURE.
measure it by %EL or %RA |
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Term
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Definition
toughness is the ENERGY to BREAK a unit volume of material. approximate by the area under the stress-strain curve
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Term
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Definition
hardness is RESISTANCE TO PERMANENTLY INDENTING THE SURFACE.
large hardness means:
- resistance to plastic deformation or cracking in compression.
- better wear properties |
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Term
| 2 ways to measure hardness |
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Definition
hardness measurement:
ROCKWELL
HB = BRINELL HARDNESS |
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Term
| Why do "true" stress and strain exist? |
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Definition
| Cross sectional area changes when sample is stretched |
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Term
Stress measures _____
Strain measures _____ |
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Definition
Stress measures LOAD
Strain measures DISPLACEMENT
(both size independent measures) |
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Term
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Definition
Hardening is an INCREASE in YIELD STRENGTH
due to PLASTIC DEFORMATION. |
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Term
| Elastic modulus is a _____ property. |
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Definition
Elastic modulus is MATERIAL property
• Critical properties depend largely on sample flaws (defects,
etc.). Large sample to sample variability. |
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Term
| Describe dislocation motion in metals. |
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Definition
• Metals (Cu, Al):
Dislocation motion EASIEST
- non-directional bonding
- close-packed directions
for slip |
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Term
| Describe dislocation motion in covalent ceramics. |
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Definition
• COVALENT Ceramics (Si, diamond)
Motion DIFFICULT
- directional (angular) bonding |
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Term
| Describe dislocation motion in ionic ceramics. |
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Definition
• Ionic Ceramics (NaCl):
Motion DIFFICULT
- need to avoid nearest
neighbors of like sign (- and +) |
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Term
Metals - plastic deformation occurs by ____ – an edge
dislocation (extra half-plane of atoms) slides over adjacent
plane half-planes of atoms. |
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Definition
Metals - plastic deformation occurs by SLIP – an edge
dislocation (extra half-plane of atoms) slides over adjacent
plane half-planes of atoms. |
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Term
| If dislocations ___ ____, plastic deformation doesn't occur! |
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Definition
| If dislocations CAN'T MOVE, plastic deformation doesn't occur! |
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Term
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 |
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Definition
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 |
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Term
Slip System
– Slip plane - plane on which ______ slippage occurs
• Highest _____ densities (and large interplanar spacings)
– Slip directions - directions of _____ movement
• Highest _____ densities |
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Definition
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 |
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Term
| What is meant by resolved shear stress? τR |
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Definition
What is meant by resolved shear stress? τR
results from applied tensile stresses -- factors in the angles between the applied stress and the slip direction & slip plane normal
Condition for dislocation motion: τR > τCRSS (Critcally resolved shear stress)
τR = δ*cosλ*cosΦ
τR maximum at Φ = λ = 45 degrees
__________________________________________
δ = applied tensile stress = F/A
λ = angle between F and slip direction (Fs)
Φ = angle between F and slip plane normal (As) |
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Term
For deformation to occur the _____ stress must
be greater than or equal to the ______ stress |
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Definition
For deformation to occur the APPLIED stress must
be greater than or equal to the YIELD stress |
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Term
SLIP MOTION in POLYCRYSTALS
• Polycrystals stronger than single crystals – ____ _____ are barriers to dislocation motion.
• Slip planes & directions (λ, Φ) change from one grain to another.
• ____ will vary from one grain to another.
• The grain with the ______ τR yields first.
• Other (less favorably oriented) grains yield later. |
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Definition
SLIP MOTION in POLYCRYSTALS
• Polycrystals stronger than single crystals – GRAIN BOUNDARIES are barriers to dislocation motion.
• Slip planes & directions (λ, Φ) change from one grain to another.
• τR will vary from one grain to another.
• The grain with the LARGEST τR yields first. • Other (less favorably oriented) grains yield later. |
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Term
| Four Strategies for Strengthening: |
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Definition
Four Strategies for Strengthening:
1: Reduce Grain Size
2: Form Solid Solutions
3: Precipitation Strengthening
4: Cold Work (Strain Hardening) |
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Term
| Why would we want to Reduce Grain Size |
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Definition
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. |
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Term
| Why would we want to Form Solid Solutions |
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Definition
2: Form Solid Solutions
- strategy for STRENGTHENING
- IMPURITY ATOMS DISTORT the lattice & generate lattice STRAINS.
- These strains can act as barriers to dislocation motion. |
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Term
- 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 |
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Definition
- 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 |
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Term
| Alloying increases _____ strength and _____ strength |
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Definition
| Alloying increases YIELD strength and TENSILE strength |
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Term
| Why is Precipitation Strengthening useful |
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Definition
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 |
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Term
| What are the 4 common forming operations that reduce the cross sectional area during Cold Work (Strain Hardening) |
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Definition
• 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 |
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Term
| How does the dislocation structure change during cold working? |
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Definition
Dislocations entangle with one another during cold work.
• Dislocation motion becomes more difficult. |
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Term
What happens to
- yield strength
- tensile strength
- ductility
as cold work is INCREASED |
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Definition
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 |
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Term
| Effect of heat treating after cold work? |
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Definition
Heat treating after cold work...
• 1 hour treatment at Tanneal...
decreases TS and increases %EL.
• Effects of cold work are nullified! |
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Term
| What are the 3 annealing stages? |
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Definition
3 Annealing stages:
1. Recovery
2. Recrystallization
3. Grain growth |
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Term
| The 1st step of annealing, RECOVERY, does what? |
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Definition
| RECOVERY REDUCES the number of DISLOCATIONS |
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Term
| The 2nd step of annealing, RECRYSTALLIZATION, does what? |
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Definition
RECRYSTALLIZATION forms new grains that:
- have LOW dislocation densities
- are SMALL in size
- consume and replace parent cold-worked grains |
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Term
| The 3rd step of annealing, GRAIN GROWTH, does what? |
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Definition
GRAIN GROWTH:
at longer times, average grain size increases
- small grains shrink and ultimately disappear
- large grains continue to grow |
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Term
TR = RECRYSTALLIZATION TEMPERATURE = temperature at which recrystallization just reaches completion in ___.
0.3Tm < TR < 0.6Tm
For a specific metal/alloy, TR depends on:
• %CW -- TR DECREASES with _____ %CW
• Purity of metal -- TR DECREASES with _____ purity |
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Definition
TR = RECRYSTALLIZATION TEMPERATURE = temperature at which recrystallization just reaches completion in 1 HOUR.
0.3Tm < TR < 0.6Tm
For a specific metal/alloy, TR depends on:
• %CW -- TR DECREASES with INCREASING %CW
• Purity of metal -- TR DECREASES with INCREASING purity |
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Term
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. |
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Definition
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. |
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Term
Ductile fracture
– Accompanied by significant _____ deformation
Brittle fracture
– Little or no _____ deformation
– Catastrophic |
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Definition
Ductile fracture
– Accompanied by significant PLASTIC deformation
Brittle fracture
– Little or no PLASTIC deformation
– Catastrophic |
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Term
| Ductile vs Brittle Failure (picture it) |
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Definition
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Term
| Ductile fracture is usually ____ desirable than brittle fracture |
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Definition
| Ductile fracture is usually MORE desirable than brittle fracture |
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Term
• Ductile failure:
-- [one/many] piece(s)
-- [small/large] deformation(s)
• Brittle failure:
-- [one/many] piece(s)
-- [small/large] deformation(s) |
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Definition
• Ductile failure:
-- ONE piece
-- LARGE deformation
• Brittle failure:
-- MANY pieces
-- SMALL deformations |
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Term
Brittle fracture surfaces:
1. ______ (between grains)
2. ______ (through grains) |
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Definition
Brittle fracture surfaces:
1. INTERGRANULAR (between grains)
2. TRANSGRANULAR (through grains) |
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Term
| Moderately ductile failure stages |
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Definition
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Term
| TS engineering materials [>>/<<] TS perfect materials |
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Definition
| TS engineering materials << TS perfect materials |
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Term
DaVinci (500 yrs ago!) observed...
-- the longer the wire, the smaller the load for failure.
• Reasons:
--
-- |
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Definition
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! |
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Term
| _____ are stress concentrators! |
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Definition
| FLAWS are stress concentrators! |
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Term
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 |
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Definition
Cracks having SHARP tips propagate EASIER than cracks having BLUNT tips
BRITTLE materials have sharp crack tips
DUCTILE materials have blunt crack tips |
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Term
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 |
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Definition
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 |
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Term
| what will cause a crack to propagate? |
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Definition
Crack propagates if crack-tip stress (δm) EXCEEDS a critical stress (δc)
the critical stress is that equation with a = half length of internal crack & specific surface energy & modulus of elasticity |
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Term
| How do we find out how much energy goes into failing a material? (Hint: A mechanical way of measuring toughness) |
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Definition
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 |
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Term
| Toughness can change depending on ductile-to-brittle transition temperature (DBTT) |
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Definition
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) |
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Term
Fatigue = failure under applied ____ stress.
Stress varies with ____.
• Key points: Fatigue...
--can cause part failure, even though δmax < δy.
--responsible for ~ 90% of mechanical engineering failures. |
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Definition
Fatigue = failure under applied CYCLIC stress.
Stress varies with TIME.
• Key points: Fatigue...
--can cause part failure, even though δmax < δy.
--responsible for ~ 90% of mechanical engineering failures. |
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Term
Types of fatigue behavior:
S = STRESS AMPLITUDE
- Fatigue limit, Sfat:
--no fatigue if S [] Sfat
- For some materials, there is no fatigue limit! (Al) |
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Definition
Types of fatigue behavior:
S = STRESS AMPLITUDE
- Fatigue limit, Sfat:
--no fatigue if S < Sfat
- For some materials, there is no fatigue limit! (Al) |
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Term
Cracks grow incrementally:
-- crack grows faster as
• change in stress [increases/decreases]
• _____ gets longer
• loading freq. [decreases/increases]. |
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Definition
Cracks grow incrementally:
-- crack grows faster as
• change in stress INCREASES
• CRACK gets longer
• loading freq. INCREASES. |
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Term
Improving fatigue life:
1.
2. |
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Definition
Improving fatigue life:
1. Impose compressive surface stresses (to SUPPRESS SURFACE CRACKS FROM GROWING)
2. Remove stress concentrators (AVOID SHARP EDGES) |
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Term
Primary Creep: slope (creep rate) _____ with time.
Secondary Creep: steady-state
i.e., constant slope (△Ɛ/△t).
Tertiary Creep: slope (creep rate)
_____ with time, i.e. _____ of rate. |
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Definition
Primary Creep: slope (creep rate) DECREASES with time.
Secondary Creep: steady-state
i.e., constant slope (△Ɛ/△t).
Tertiary Creep: slope (creep rate)
INCREASES with time, i.e. ACCELERATION of rate. |
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Term
Creep is temperature dependent
Occurs at elevated temperature, T > ___ Tm (in K) |
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Definition
Creep is temperature dependent
Occurs at elevated temperature, T > 0.4 Tm (in K) |
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Term
Secondary Creep:
Strain rate is _____ at a given T, δ
strain rate increases with _____ T, δ |
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Definition
Secondary Creep:
Strain rate is CONSTANT at a given T, δ
strain rate increases with INCREASING T, δ |
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Term
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. |
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Definition
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. |
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Term
Ceramics:
compounds of ____ and _____ elements |
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Definition
Ceramics:
compounds of METALLIC and NON-METALLIC elements
e.g. Al2O3, ZrO2, MgO, TiO2, SiC, WC, B4C, ZnS, TiB2 and carbon… |
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Term
_______ ceramics:
- china, porcelain, bricks, tiles, glasses
- many based on clays
______ ceramics - oxides, carbides, nitrides
- used in electronics, computers, aerospace… |
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Definition
TRADITIONAL ceramics:
- china, porcelain, bricks, tiles, glasses
- many based on clays
TECHNICAL ceramics - oxides, carbides, nitrides
- used in electronics, computers, aerospace… |
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Term
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 |
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Definition
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 |
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Term
Ceramic bonding:
-- Mostly _____ with varying degrees of ____.
-- % ionic character increases with difference in
_____ of atoms. |
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Definition
Ceramic bonding:
-- Mostly IONIC with varying degrees of COVALENCY.
-- % ionic character increases with difference in
ELECTRONEGATIVITY of atoms. |
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Term
(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 |
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Definition
(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 |
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Term
Key factors influencing ceramic structure:
1.
2. |
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Definition
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 |
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Term
Non-metallic anions (-) much ____ than metallic cations (+)
• Pack like atoms in metals
______ metallic cations may thus fit into the spaces (i.e. the
_____ sites) |
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Definition
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) |
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Term
| What are the two possible types of ceramic interstitial sites? Give some info on both. |
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Definition
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 |
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Term
| What determines which site the cations will occupy? |
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Definition
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 |
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Term
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 |
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Definition
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 |
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Term
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 |
|
Definition
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 |
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Term
List the AX-Type crystal structures
AX-Type means EQUAL # of cations and anions |
|
Definition
List the AX-Type crystal structures:
1. NaCl (ROCK SALT)
2. CsCl (Cesium Chloride) |
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Term
Describe NaCl (ROCK SALT) structure:
- can be considered as 2 interpenetrating ___ lattices: one of cations and one of anions
- CN = __
- cations prefer ____ sites |
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Definition
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 |
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Term
Describe CsCl (Cesium Chloride) structure:
- Each ion has __ neighbors
- ___ sites preferred
- like a ___ but not ___ since there are two different kind of ions. |
|
Definition
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. |
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Term
Describe Zinc Blende (ZnS) structure:
- small Zn cations sit between __ S anions, CN = __
- Happens when .225- Zn is in the ____ interstitial site
- __ of the possible ______ sites are occupied
- The bonding is usually highly ______ |
|
Definition
Describe Zinc Blende (ZnS) structure:
- small Zn cations sit between 4 S anions, CN = 4
- Happens when .225- Zn is in the TETRAHEDRAL interstitial site
- 4 of the possible TETRAHEDRAL sites are occupied
- The bonding is usually highly COVALENT (ZnS, ZnTe, SiC). |
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Term
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 |
|
Definition
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 |
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Term
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 |
|
Definition
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 |
|
|
Term
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. |
|
Definition
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. |
|
|
Term
______:
- 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 |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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) |
|
|
Term
• ____ Defect
-- a paired set of cation and anion vacancies.
• ____ Defect
-- a cation vacancy-cation interstitial pair. |
|
Definition
• SHOTTKY Defect
-- a paired set of cation and anion vacancies.
• FRENKEL Defect
-- a cation vacancy-cation interstitial pair. |
|
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Term
| _________ must be maintained when impurities are present |
|
Definition
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) |
|
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Term
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. |
|
Definition
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. |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
| In general, why do ceramics fail? |
|
Definition
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. |
|
|
Term
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 ____. |
|
Definition
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. |
|
|
Term
____ _____ 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 |
|
Definition
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 |
|
|
Term
| Modulus of rupture, DELTAr is larger than tensile strength for two reasons: |
|
Definition
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. |
|
|
Term
| Give 3 examples of applications for ceramics |
|
Definition
Give 3 examples of applications for ceramics
1. DIE BLANKS
2. CUTTING TOOLS
3. SENSORS |
|
|
Term
|
Definition
| Refractories are materials to be used at HIGH TEMPERATURES. |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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 ____ ____ |
|
Definition
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. |
|
|
Term
|
Definition
poly = many
mer = repeat unit |
|
|
Term
• Originally natural polymers were used
– Wood – Rubber
– Cotton – Wool
– Leather – Silk
• Oldest known uses
– Rubber balls used by Incas
– Woven cloth |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
Most polymers are ______
– i.e., made up of H and C |
|
Definition
Most polymers are HYDROCARBONS
– i.e., made up of H and C |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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. |
|
Definition
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. |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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 _____ |
|
Definition
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 |
|
|
Term
Chain Repeat Units
– If all the same: _____
– If different: _____ |
|
Definition
Chain Repeat Units
– If all the same: HOMOPOLYMERS
– If different: COPOLYMERS |
|
|
Term
_______ 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: _____ |
|
Definition
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 |
|
|
Term
________ polymerization
– Intermolecular reactions involving >1 monomer species giving off a low MW condensate (e.g. H2O)
– E.g. Nylon 6,6 |
|
Definition
CONDENSATION polymerization
– Intermolecular reactions involving >1 monomer species giving off a low MW condensate (e.g. H2O)
– E.g. Nylon 6,6 |
|
|
Term
______ ______ Polymer (3-D Crosslinking)
– Phenol-Formaldehyde (Phenolic) |
|
Definition
THERMOSET NETWORKED Polymer (3-D Crosslinking)
– Phenol-Formaldehyde (Phenolic) |
|
|
Term
|
Definition
ISOMERISM:
– Two compounds with same chemical formula can have quite different structures
ex. C8H18 can be normal octane or 2,4-dimethylhexane |
|
|
Term
| Thermoplastics vs. Thermosets |
|
Definition
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. |
|
|
Term
Not all chains in a polymer are of the same ____
— i.e., there is a distribution of molecular weights |
|
Definition
Not all chains in a polymer are of the same LENGTH
— i.e., there is a distribution of molecular weights |
|
|
Term
• MW can be defined in several ways:
• Number averaged, |
|
Definition
| DP = average number of repeat units per chain |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
Physical characteristics of polymers depend on:
1.
2.
3. |
|
Definition
Physical characteristics of polymers depend on:
1. MOLECULAR WEIGHT
2. SHAPE
3. STRUCTURE |
|
|
Term
| List the 4 covalent chain configurations in order of increased strength |
|
Definition
|
|
Term
• Linear polymer:
‒ Repeat units joined end-to-end
‒ Long flexible chains (“spaghetti”)
‒ Extensive _____ and ____ bonds betweenchains
‒ PE, PVC, PS, MPPA, Nylon, fluorocarbons |
|
Definition
• 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 |
|
|
Term
Branched polymer:
• Side-branch chains connected to main chain
• Chain packing efficiency ____
• ____ density
• LDPE |
|
Definition
Branched:
• Side-branch chains connected to main chain
• Chain packing efficiency REDUCED
• LOWER density
• LDPE |
|
|
Term
• Crosslinked polymer:
‒ Adjacent chains joined by ____ bonds
‒ Occurs during ____
‒ Non-reversible
‒ Rubbers (via vulcanization using S atoms) |
|
Definition
• Crosslinked polymer:
‒ Adjacent chains joined by COVALENT bonds
‒ Occurs during SYNTHESIS
‒ Non-reversible
‒ Rubbers (via vulcanization using S atoms) |
|
|
Term
Network polymer:
• Monomers forming __ or more covalent bonds
• Form 3-D networks
• Epoxies, polyurethanes, phenol-formaldehyde |
|
Definition
Network polymer:
• Monomers forming 3 or more covalent bonds
• Form 3-D networks
• Epoxies, polyurethanes, phenol-formaldehyde |
|
|
Term
| ______ are mirror images – can’t superimpose without breaking a bond |
|
Definition
| STEREOISOMERS are mirror images – can’t superimpose without breaking a bond |
|
|
Term
| Configurations – to change must ____ ____ |
|
Definition
| Configurations – to change must BRAEAK BONDS |
|
|
Term
______ – 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 |
|
Definition
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 |
|
|
Term
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? |
|
Definition
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 |
|
|
Term
| What are 4 possible arrangements for copolymers (two or more monomers polymerized together) |
|
Definition
|
|
Term
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) |
|
Definition
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) |
|
|
Term
How does an increase in % crystallinity of a polymer affect:
TS and E
How does heat treating affect % crystallinity? |
|
Definition
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 |
|
|
Term
| Single polymer crystals – only for ____ and carefully ____ growth rates |
|
Definition
| Single polymer crystals – only for SLOW and carefully CONTROLLED growth rates |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
| Strengths of polymers ~__% of those for metals |
|
Definition
| Strengths of polymers ~10% of those for metals |
|
|
Term
| Picture the deformation of BRITTLE crosslinked and network polymers |
|
Definition
|
|
Term
| Picture the deformation of SEMICRYSTALLINE (PLASTIC) polymers |
|
Definition
|
|
Term
| Picture the deformation of ELASTOMERS |
|
Definition
|
|
Term
| What does the stress strain curve look like for BRITTLE polymers, PLASTIC polymers, and ELASTOMERS |
|
Definition
|
|
Term
Influence of T on Thermoplastics:
Decreasing T...
-- ____ E
-- ____ TS
-- ____ %EL |
|
Definition
Influence of T on Thermoplastics:
Decreasing T...
-- INCREASES E
-- INCREASES TS
-- DECREASES %EL |
|
|
Term
Influence of strain rate on Thermoplastics:
Increases strain rate...
-- ____ E
-- ____ TS
-- ____ %EL |
|
Definition
Influence of strain rate on Thermoplastics:
Increases strain rate...
-- INCREASES E
-- INCREASES TS
-- DECREASES %EL |
|
|
Term
|
Definition
Tm = MELTING TEMP
Tg = GLASS TRANSITION TEMP |
|
|
Term
| What factors affect Tm and Tg? |
|
Definition
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 |
|
|
Term
| How can we increase chain stiffness, in turn increasing Tm and Tg? |
|
Definition
Chain stiffness increased by presence of
1. Bulky sidegroups
2. Polar groups or sidegroups
3. Chain double bonds and aromatic chain groups |
|
|
Term
| Regularity of repeat unit arrangements – affects [Tm/Tg] only |
|
Definition
| Regularity of repeat unit arrangements – affects Tm only |
|
|
Term
Craze formation prior to cracking:
– during crazing, plastic deformation of spherulites
– and formation of ____ and ____ bridges |
|
Definition
Craze formation prior to cracking:
– during crazing, plastic deformation of spherulites
– and formation of MICROVOIDS and FIBRILLAR bridges |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
| List 4 methods of processing polymers and which type (thermoplastic or thermoset) it applies to |
|
Definition
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 |
|
|
Term
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 |
|
Definition
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 |
|
|
Term
| polymer fiber characteristics |
|
Definition
polymer fiber characteristics
1. high tensile strengths
2. high degrees of crystallinity
3. structures containing polar groups |
|
|
