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[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt1
Bruce Mayer, PE Engineering-45: Materials of Engineering
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 45
PolymerApplicatio
ns
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt2
Bruce Mayer, PE Engineering-45: Materials of Engineering
Learning Goals – Polymer Apps
Learn How Microstructure affects Room Temperature Tensile Stress Behavior
Understand Hardening, Anisotropy, and Annealing in Polymers
How the elevated-temperature mechanical-response for PolyMers compares to Ceramics and Metals
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt3
Bruce Mayer, PE Engineering-45: Materials of Engineering
PolyMer Tensile σ-ε Response
PolyMers Exhibit 3 Basic Types of Tensile ResponseA. Brittle → Glass-
Like• Linear-Elastic• Very Small Strain
at Fracture
B. Elastic-Plastic → Metal-Like• Well-Defined
Yielding• Significant Strain
at Fracture
C. Elastomeric → Rubber-Like• Completely
Elastic; all the way to fracture
• Very Large Strains
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt4
Bruce Mayer, PE Engineering-45: Materials of Engineering
Tensile Response – Brittle & Plastic
0
unload/reload
0
brittle failure
plastic failure
20
40
60
2 4 6
s (MPa)
e
x
x
semi- crystalline
case
amorphous regions
elongate
crystalline regions align
crystalline regions
slide
8
onset of necking
aligned, cross- linked case
networked case
Initial
Near Failure
near failure
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt5
Bruce Mayer, PE Engineering-45: Materials of Engineering
Tensile Response – Elastomers
Compare Elastomers to responses of other polymers:• BRITTLE response (aligned, cross-linked & networked case)• PLASTIC response (semi-crystalline case)
initial: amorphous chains are kinked, heavily cross-linked.
final: chains are straight,
still cross-linked
0
20
40
60
0 2 4 6
s (MPa)
e 8
x
x
x
elastomer
plastic failure
brittle failure
Deformation is reversible!
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt6
Bruce Mayer, PE Engineering-45: Materials of Engineering
T & StrainRate - ThermoPlastics
DEcreasing Temp• Increases E• Increases TS• Decreases %EL
INcreasing Strain Rate...• Same effects as decreasing Temperature20
40
60
80
00 0.1 0.2 0.3
4°C
20°C
40°C
60°C
to 1.3
s (MPa)
e
Data for the semicrystalline polymer: PMMA (Plexiglas)
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt7
Bruce Mayer, PE Engineering-45: Materials of Engineering
PreDeformation by Drawing Drawing
• stretches the polymer prior to use• aligns chains to the stretching direction
Results of drawing• Increases the elastic modulus (E) in the
stretching direction• Increases the tensile strength (TS) in the
stretching direction• Decreases ductility (%EL)
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt8
Bruce Mayer, PE Engineering-45: Materials of Engineering
Vulcanization Chemically Induced Cross-Linking Process in
Elastomers is called VULCANIZATION• An Irreversible Chemical Reaction Performed at
Elevated Temperature Thru a Cross Linking Agent; Typically Sulfur
Typically Requires More than ONE S-atom per Cross-Link
Vulcanization at the 1-5 wt%-S level improves Elastomer Properties Including Wear & Strength (e.g., Tires)
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt9
Bruce Mayer, PE Engineering-45: Materials of Engineering
Time Dependent Deformation
Stress Relaxation Test• Rapidly deform to
Strain ε0, and Hold
• Measure Hold-Stress as a Function of Time
time
strain
tensile test
o
t( )
The Hold-Stress Decreases with Time Due to “unkinking” of the PolyMer chains
/0)( tet
• Where– σ0 Stress at time-0
– Time Constant; i.e., the time required for the stress to drop by 63%
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt10
Bruce Mayer, PE Engineering-45: Materials of Engineering
Relaxation Modulus
Given Stress Relaxation
time
strain
tensile test
o
t( )
Next Pick a BaseLine time, Say 10s, and Vary Temperature to
or
ttE
)(
)(
Define a Time-Dependent RELAXATION Modulus Ttempo
r
sTE
)10()(10
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt11
Bruce Mayer, PE Engineering-45: Materials of Engineering
Relaxation Modulus vs Temperature
Glassy State• Material is RIGID and
BRITTLE• ELASTIC Stretching of
Bonds
Leathery State• some Sliding of chains
over one another• some Permanent
deformation• deformation will be time-
dependent and not totally recoverable
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt12
Bruce Mayer, PE Engineering-45: Materials of Engineering
Relaxation Modulus vs Temp cont.1
Rubbery Plateau• deforms in a
rubbery manner• both elastic and
viscous behavior• straightening out of
polymer chains gives large strains
• strain is reversible due to crosslinks and entanglements
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt13
Bruce Mayer, PE Engineering-45: Materials of Engineering
Relaxation Modulus vs Temp cont.2
Rubbery flow and Viscous flow• high temperature states• polymer chains slide
over each other• permanent deformation
is possible (molding)
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt14
Bruce Mayer, PE Engineering-45: Materials of Engineering
Glass Transition Temperature
Notice on the Er
vs T curve the almost VERTICALSlope at the Centerof the Leathery, orTough Regime
This marks the Transition from a Brittle, amorphous State to a ViscoElastic Condition
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt15
Bruce Mayer, PE Engineering-45: Materials of Engineering
The Glass Transition Temp
Temperature
Sp
ecifi
c V
olu
me =
1/ρ
(cu
-m/k
g)
Tg Tm
Note Change in
Slope
NonCrystalline Material• T < Tg → Rigid, Glass-Like• Tg < T < Tm → Rubbery
or Leathery• T > Tm → Melted, Liquid
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt16
Bruce Mayer, PE Engineering-45: Materials of Engineering
Structure-Property Relationships
Ease of MOVEMENT of molecular chains affects properties• crystallinity (ability to pack efficiently)• Tg (onset of
large-scale molecular motion)
• Glass-forming ability
• Strength vs. Flexibility
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt17
Bruce Mayer, PE Engineering-45: Materials of Engineering
Structure-Property Relns cont.
STRUCTURAL factors that inhibit molecular motion:• Complexity of the Mer• Size of Side Groups• Branching,
Crosslinking• Configuration• Bonding • Entanglements
Possible organization of PolyEthylene polymer chains
CrystallineRegion
Amorphous Tie Region
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt18
Bruce Mayer, PE Engineering-45: Materials of Engineering
WhiteBoard Work
Prob Similar to 15.24 Vulcanize PolyIsoPrene with Sulfur
• Given – 57 wt%-S combined with the polymer– Six Sulfur atoms per CrossLink on Average
• Determine CrossLinks per Isoprene Mer
Natural rubber (cis-polyisoprene) before vulcanizing
with sulfur
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt19
Bruce Mayer, PE Engineering-45: Materials of Engineering
IsoPrene Polymerization
[email protected] • ENGR-45_Lec-30_Polymer-Apps.ppt20
Bruce Mayer, PE Engineering-45: Materials of Engineering
σ-ε vs. T for FluoroPolymer