BK50A2700 Selection Criteria of Structural Materials
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Transcript of BK50A2700 Selection Criteria of Structural Materials
BK50A2700 Selection Criteria of Structural Materials
Lesson 52014
Selection of polymers
Lesson 52014
The goal of this lesson
Our goal is, that after this lesson, students are able to recognize the key criteria for selecting polymers and are able to use different tools to support the systematic material selection process for proper selection of polymers.
Outline
Selection of
Polymers
Special material
properties
Temperature related selection criteria
Tools for systematic selection
Viewpoints of
Chemistry
Special material properties
Special materials properties affecting to proper selection of polymers:
• 1. Glass transition temperature• 2. Shape of the stress-strain curve• 3. Viscoelastic behavior• 4. Creeping strength and heat
deflection temperature • 5. Fatigue strength and grazing • 6. Impact strength and brittleness temperature • 7. Ageing
-sunlight, chemicals• 8 .Stress cracking
- residual stresses due to manufacturing- environmental reasons (e.g. some
chemicals)
Fracture mechanisms of polymers
Both ductile and brittle fracture are possible.
Brittle fracture is favored at lower temperatures, higher strain rates, and at stress concentrators
Brittle to ductile transition often occurs with increasing temperature
The third “fracture mechanism is called “crazing “…
Crazing occurs when localized regions yield, forming microvoids inside polymer chain structure.
Fibrillar bridges or fibrils are formed around and between voids.Crazing absorbs fracture energy and increases fracture toughness
Fibrilsin polymer chains
Microvoids
Fibrilsin polymer chains
Microvoids
Strain
Strain
Relative elongation [%]
Stress [MPa]
Linear or non-linear plastic deformation
Reduction of the cross-section area
Plastic deformation
Ultimate tensile strength
Yeld strength
Viscoelasticity:Viscoelastic behavior is determined by rate of strain: elastic for rapidly applied stress, viscous for slowly applied stress!
Viewpoints of Chemistry
POLYMERS
POLYMERIZATION CHARACTERISTICS OF POLYMERS (TYPES)
THERMOPLASTIC
CONDENSATION POLYMERIZATION
THERMOSEPTIC
TYPES OF POLYMERCHAINS
ADDITION POLYMERIZATION
ELASTOMERS
CARBON-HYDROGEN POLYMERS (PE)
CARBON-CHAIN POLYMERS (PTFE)
HETEROCHAIN POLYMERS (PA)
POLYMER CONSTRUCTIONS WITH THE AROMATIC RINGS IN THE CHAIN (Kevlar)
AMIDI-GROUP
Polymerization
• 1. Addition is a chain-reaction, where monomer units are attached one at a time. E.g. PVC.
• 2. Condensation is a step reaction, which produce the mer units. Usually there is small by-product that is later eliminated. E.g. PA.
• Note: Polymers manufactured with condensation polymerization absorb easily water, which can damage their structure relatively soon!
Effects of the chemical structure on the polymers` properties
Structure and bonding of mers
Molecular structure
Stereo isometric forms
Double bonded (c=c)
Number of monomers
Construction of the polymer chain
Single bonded (c-c)
Co-polymers
LINEAR
CROSS-LINKED
Aromatic ringsIsotactic
Syndiotactic
Eutactic
TACTICITY
Heterotactic
Atactic
BRANCHED
DENSITY
Low-density LD
High-density HD
Medium-density MD
Linear low-density LDD
Ultra high- molecular weight (UHMW)
Homo-polymers
Bonding between
the atoms
Bonding energykJ/mol
C-C 350
C-H 410
C-F 440
C-Cl 330
C-O 350
C-S 260
C-N 290
N-N 160
N-H 390
O-H 460
C = C 810
C = O 715
C = N 615
AFFECTS OF BONDING BETWEEN MERS
N
NO
O
H
Hn
H
OH
CHEMICAL STRUCTURE OF KEVLAR
AROMATIC RING
CH3 CH3 CH3 CH3 CH3 CH3 METHYLENE GROUPS
HIGH STRENGTH OF THE STRUCTURE
CH3 CH3 CH3 HIGH STIFFNESS AND RIGIDITY OF THE STRUCTURE
CH3 CH3 CH3
METHYLENE GROUPS
METHYLENE GROUPS
AFFECTS OF STEREOISOMETRIC FORMS (TACTICITY)
Density classification
Property LDPE LLDPE HDPE
Mass (g/cm³) 0,92-0,93
0,922-0,926
0,95-0,96
Tensile strenght (GPa) 6,2-17,3 12,4-20,0 20,0-37,3
Elongnation to rupture % 550-600 600-800 20-120
AFFECTS OF DENSITY
HDPE
LDPE
LLDPE
STRENGHT INCREASES
Amorfic polymers
Semicrystalline polymers
Elastomers
General polymers
Engineering polymers
High-performancepolymers
Ultra high-performancepolymers
PVC, PS
PEI, PSU
PC, ABS, PMMA
PIPEI
PP ,PE
PET, POM ,PA
PTFE, PPAPPS, PFA
PEEKPAI
NBR
EPR, EVA
FKM
PFPE
75 ºC
140 ºC
240 ºC
340 ºC
Temperature related selection criteria
ASPECTS AFFECTING
THE CRITICAL TEMPERATURE OF POLYMERS
Creeping strength at the specific temperature
Decomposition temperature of the polymer chain
Melting point
Required temperature during the manufacturing process
Fatigue strength at the specific temperature
Maximum operating temperature
Heat deflection temperature (load is
specified)
Glass transition temperature
Viscoelastic behavior related to temperature and impact forces
Brittleness temperature
Polymer degradation due to overheating
Minimum operating temperature
E(Modulus of elasticity)
Tglass transition Tmelting T (Temperature)
Glassy state
Leathery state
Rubbery flow
Liquid flow
Modulus of elasticity of polymers depending on temperature
Rigid state
Viscoelasticity : - glass at low temperatures- rubber at intermediate
temperatures- viscous liquid at high
temperatures.Viscoelastic behavior is determined by rate of strain(elastic for rapidly applied stress, viscous for slowlyapplied stress)
Examples of glass transition temperatures for some polymers
STRESS[MPa)
TIME NEEDED TO FRACTURE
[h]
TEMPERATURE
23ºC
70ºC
100ºC
1 100 10000
GREEPING STRENGTH
Many polymers susceptible to time-dependentdeformation under constant load – viscoelastic creepCreep may be significant even at room temperatureand under moderately low stresses (below yieldstrength).
PolymerHeat deflection temperature °C
(under 1.8 MPa loading)
Polyethylene (UHDPE) 40
Polypropylene (PP) 60
Polyamide (PA6,6 + nylon) 90
Polyamide-imide (PAI) 280
Tools for systematic selection
IMPACT STRENGTH
ULTIMATE TENSILE STRENGTH
MAX. OPERATING
TEMPERATURE
PI
PI
MIN. OPERATING
TEMPERATURE
PC
PC
PC+ glass-fiber
UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION
PC+ glass-fiber
Rejectedarea
RESISTANCE AGAINST ALCALINE AGENTS
RESISTANCE AGAINST ACID AGENTS
RESISTANCE AGAINST ORGANIC
SOLVENTS
1
WATER ABSORBTION
PTFE
PTFE
PTFE
PTFE
PIPI
PI
PI
UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION
Requiredarea
UTILIZATION OFCOBWEB-ANALYSIS FOR POLYMERS’ SELECTION
WEAR RESISTANCE
COMPRESSIONSTRENGTH
1B
1A
3C 3A
2A
2B
Required wear resistance
Required strength
Accepted area
Polymer
Max. / Min. operating
temperature
[ °C] / [ °C]
Glass deformatio
n temperatur
e[ °C]
Heat deflection
temperature
[ °C]
Brittleness temperatur
e
[ °C]
Creeping strength at
X °C[MPa]
Processing temperatur
e
[ °C]
Option 1Required range: [ °C] / [ °C]
Material property: [ °C] / [ °C]
Affecting load: [ MPa / °C]
Material property: [ MPa] / °C]
Energy costs:[€]
Option 2Required range: [ °C] / [ °C]
Material property: [ °C] / [ °C]
Affecting load: [ MPa / °C]
Material property: [ MPa] / °C]
Energy costs:[€]
Option 3Required range: [ °C] / [ °C]
Material property: [ °C] / [ °C]
Affecting load: [ MPa / °C]
Material property: [ MPa] / °C]
Energy costs:[€]
Option 4Required range: [ °C] / [ °C]
Material property: [ °C] / [ °C]
Affecting load: [ MPa / °C]
Material property: [ MPa] / °C]
Energy costs:[€]
COMPARISON TABLE TO FIT THE MATERIAL PROBERTIES WITH REQUIREMENTS
PA Polyamide (Nylon) - Minlon® PA
- Zytel® PA
PA 11 Polyamide 11
PA 12 Polyamide 12
PA 46 Polyamide 46
PA 6 Polyamide 6 - Minlon® PA
- Zytel® PA
PA 6 / 12 Polyamide 6 / Polyamide 12
PA 6 / 66 Polyamide 6 / Polyamide 66 -Zytel® PA
PA 6 / 69 Polyamide 6 / Polyamide 69
PA 6 / 6T Polyamide 6 / Polyamide 6t
PA 610 Polyamide 610
PA 612 Polyamide 612
PA 6-3-T Polytrimethylene Hexamethylene Terephthalamide
PA 66 Polyamide 66 - Minlon® PA
- Zytel® PA
PA 66 / 6 Polyamide 66 / Polyamide 6 - Zytel® PA
PA 66 / 610
Polyamide 66 / Polyamide 610
PA 68 Polyamide 68
Amidegroup
HDPE High Density Polyethylene - Rigidex® Polyethylene
- Eraclene® LDPE - TIPELIN® HDPE
LDPE Low Density Polyethylene - INEOS LDPE - Riblene® LDPE
- Borstar Polyolefin - Ipethene® LDPE
- TIPOLEN® LDPE
LLDPE Linear Low Density Polyethylene
PEHD High-Density Polyethylene - Eraclene® HDPE - ExxonMobil™ HDPE
- Rigidex® Polyethylene
- TIPELIN® HDPE
UHMWPE Ultrahigh Molecular Weight Polyethylene
ULDPE Ultra Low Density Polyethylene
-Clearflex® LLDPE
Applications from mechanical engineerig:Polymer gears:
High Performance Polymers (PEEK,PES,PI) Harsh loading conditions
Polyasetal POM Good fatigue strength
Polyamide PA Good adhesive wear resistance
Phenol polymers, e.g. PF Cost-effectiveness
Sliding bearings: Polyamide PA, Polyethylene PE, Teflon (small
friction coefficient with adjacent steel components)
The properties of polymers can be improved by reinforcing the matrix (carbon, aramid or other fibers) or by surface treatments (e.g. MoS2)
Remember the manufacturability aspects!
PolymerShrinkage during extrusion into mold %