BK50A2700 Selection Criteria of Structural Materials

1. BK50A2700 Selection Criteria of Structural Materials Lesson5 2014

2. Selection of polymers Lesson 5 2014

3. The goal of this lesson

4. 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.

5. Outline

6. Special material properties • Selection of Polymers • Viewpoints of Chemistry • Temperature related selection criteria • Tools for systematic selection

7. Special material properties

8. 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)

9. 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 “…

10. Crazing occurs when localized regions yield, forming microvoids inside polymer chain structure. Fibrillarbridges or fibrils are formed around and between voids. Crazing absorbs fracture energy and increases fracture toughness Strain Strain Microvoids Fibrils in polymer chains Microvoids Fibrils in polymer chains

11. Stress [MPa] Viscoelasticity: Viscoelastic behavior is determined by rate of strain: elastic for rapidly applied stress, viscous for slowly applied stress! Ultimate tensile strength Yeld strength Relative elongation [%] Linear or non-linear plastic deformation Reduction of the cross-section area Plastic deformation

12. Viewpoints of Chemistry

13. POLYMERS CHARACTERISTICS OF POLYMERS (TYPES) POLYMERIZATION TYPES OF POLYMERCHAINS ADDITION POLYMERIZATION CARBON-HYDROGEN POLYMERS (PE) THERMOPLASTIC THERMOSEPTIC CONDENSATION POLYMERIZATION CARBON-CHAIN POLYMERS (PTFE) ELASTOMERS HETEROCHAIN POLYMERS (PA) AMIDI-GROUP POLYMER CONSTRUCTIONS WITH THE AROMATIC RINGS IN THE CHAIN (Kevlar)

14. 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!

15. Effects of the chemical structure on the polymers` properties Construction of the polymer chain Structure and bonding of mers Molecular structure Number of monomers Co-polymers Single bonded (c-c) Stereo isometric forms LINEAR DENSITY Low-density LD BRANCHED Homo-polymers Double bonded (c=c) TACTICITY CROSS-LINKED High-density HD Isotactic Aromatic rings Syndiotactic Medium-density MD Heterotactic Atactic Linear low-density LDD Eutactic Ultra high- molecular weight (UHMW)

16. AFFECTS OF BONDING BETWEEN MERS

17. O OH H N AROMATIC RING H O N H n CHEMICAL STRUCTURE OF KEVLAR

18. AFFECTS OF STEREOISOMETRIC FORMS (TACTICITY) CH3 CH3 CH3 CH3 CH3 CH3 METHYLENE GROUPS HIGH STRENGTH OF THE STRUCTURE CH3 CH3 CH3 METHYLENE GROUPS HIGH STIFFNESS AND RIGIDITY OF THE STRUCTURE METHYLENE GROUPS CH3 CH3CH3

19. AFFECTS OF DENSITY

20. STRENGHT INCREASES HDPE LDPE LLDPE

21. 340 ºC Ultra high-performance polymers PI PEI PEEK PAI PFPE 240 ºC High-performance polymers PEI, PSU FKM PTFE, PPA PPS, PFA 140 ºC Engineering polymers EPR, EVA 75 ºC PC, ABS, PMMA General polymers PET, POM ,PA PVC, PS NBR Amorfic polymers Elastomers PP ,PE Semicrystalline polymers

22. Temperature related selection criteria

23. Maximum operating temperature Minimum operating temperature Glass transition temperature Viscoelastic behavior related to temperature and impact forces Brittleness temperature Required temperature during the manufacturing process ASPECTS AFFECTING THE CRITICAL TEMPERATURE OF POLYMERS Creeping strength at the specific temperature Melting point Heat deflection temperature (load is specified) Decomposition temperature of the polymer chain Polymer degradation due to overheating Fatigue strength at the specific temperature

24. Modulus of elasticity of polymersdepending on temperature E (Modulus of elasticity) • Viscoelasticity : • glass at low temperatures • rubber at intermediate temperatures • viscous liquid at high temperatures. Rigid state Glassy state Viscoelastic behavior is determined by rate of strain (elastic for rapidly applied stress, viscous for slowly applied stress) Leathery state Rubbery flow Liquid flow Tglass transition TmeltingT (Temperature)

25. Examples of glass transition temperatures for some polymers

26. GREEPING STRENGTH Many polymers susceptible to time-dependent deformation under constant load – viscoelastic creep Creep may be significant even at room temperature and under moderately low stresses (below yield strength). STRESS [MPa) TEMPERATURE 23ºC 70ºC 100ºC TIME NEEDED TO FRACTURE [h] 1 100 10000

28. Tools for systematic selection

29. UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION ULTIMATE TENSILE STRENGTH PC+ glass-fiber PI Rejected area PC MAX. OPERATING TEMPERATURE MIN. OPERATING TEMPERATURE PI PC+ glass-fiber PC IMPACT STRENGTH

30. UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION RESISTANCE AGAINST ACID AGENTS PTFE PTFE PI PI Required area RESISTANCE AGAINST ORGANIC SOLVENTS 1 WATER ABSORBTION PI PI PTFE PTFE RESISTANCE AGAINST ALCALINE AGENTS

31. UTILIZATION OFCOBWEB-ANALYSIS FOR POLYMERS’ SELECTION

32. WEAR RESISTANCE 1A Acceptedarea 3A Requiredwearresistance 3C 2B 2A 1B COMPRESSION STRENGTH Requiredstrength

33. COMPARISON TABLE TO FIT THE MATERIAL PROBERTIES WITH REQUIREMENTS

35. Amide group

37. 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)

38. Remember the manufacturability aspects! Shrinkage during extrusion into mold % Polymer