1. Creep Relaxation

2. Creep of cellulose acetate

3. Relaxation in PMMA 10 9 8 7 0.0010.010.11101001000 Stress relaxation of PMMA Time (hours) 40 0 C Log E(t), (dynes/cm 2 ) 60 0 C 80 0 C 92 0 C 100 0 C 110 0 C 112 0 C 115 0 C 120 0 C 125 0 C 135 0 C

4. Creep & recovery

5. Some specific polymers Polyvinyl chloride (PVC) {-C-C-} n Cl H H – – – – – – – – Very rigid and strong, T g = 60-80 C siding, pipe, conduit, usw. Very rigid and strong, T g = 60-80 C siding, pipe, conduit, usw. Presence of Cl gives rise to solubility in various organic solvents - allows "solvent welding"

6. Some specific polymers Polyvinyl chloride (PVC) {-C-C-} n Cl H H – – – – – – – – Presence of Cl gives rise to solubility in various organic solvents Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer" Presence of Cl gives rise to solubility in various organic solvents Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer" PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!

7. Some specific polymers Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer" PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"! Problem: solvent slowly evaporates, esp. when (auto) vinyl seats & fascia heated by sun Armorall to the rescue! Periodically put solvent back into polymer

8. Oils - Low MW……liquids lubricants, hydraulic fluids, water repellants, usw. Oils - Low MW……liquids lubricants, hydraulic fluids, water repellants, usw. Elastomers - intermediate MW, crosslinked waterproofing, caulk, prostheses, usw. Elastomers - intermediate MW, crosslinked waterproofing, caulk, prostheses, usw. Molding compds - high MW, crosslinked non-structural parts, insulation, usw. Molding compds - high MW, crosslinked non-structural parts, insulation, usw. Crosslinking – moisture reacts w/parts of chain to crosslink……acetic acid is byproduct of rxn Crosslinking – moisture reacts w/parts of chain to crosslink……acetic acid is byproduct of rxn silicones Some specific polymers

9. High T M – form at elevated temps Non-crystalline, nearly as strong as highly crystalline nylon, but tougher (stiff chain, pendant groups, H bonding betwn chains) {-O-C-O- -C- -} n O H-C-H H H polycarbonate Some specific polymers

10. Nylon cousin, but far stronger (very stiff chain) {-C- -C-N- -N-} n O O H H aramid O O H H Non-burning, very high T M, solvent resistant When made into fibers ––> Kevlar Some specific polymers

11. H 2 C-C-C{-O- -C- -O-} n C-C-CH 2 H-C-H H H epoxy H HOO H H hardenerH 2 N-R-NH 2 Prepregs Some specific polymers

12. Composites - overview Example - carbide tools (previously discussed) Co matrix phase angular WC fragments

13. Composites - overview Artificial combination of matrix phase & dispersed phase Artificial combination of matrix phase & dispersed phase Matrix: metal, alloy ceramic mat'l polymer Matrix: metal, alloy ceramic mat'l polymer Dispersed phase: particulate fiber Dispersed phase: particulate fiber

14. Composites - metal matrix composites (MMCs) Particulates: ThO 2 -dispersed Ni (TD Ni) sintered Al powder (SAP) Particulates: ThO 2 -dispersed Ni (TD Ni) sintered Al powder (SAP) - except strengthening maintained at hi T Improves: strength creep resistance hi T corrosion resistance Improves: strength creep resistance hi T corrosion resistance Works like precipitation hardening

15. Composites - metal matrix composites (MMCs) Fibers: Cont s - C, SiC, B, Al 2 O 3 Discont s - C, Al 2 O 3, SiC whiskers Fibers: Cont s - C, SiC, B, Al 2 O 3 Discont s - C, Al 2 O 3, SiC whiskers May get rxn betwn phases at hi T Matrix mat'ls

16. Composites - ceramic matrix composites (CMCs) Particulates, fibers: SiC, B, Al 2 O 3, C, SiC & Si 3 N 4 whiskers Particulates, fibers: SiC, B, Al 2 O 3, C, SiC & Si 3 N 4 whiskers Improve fracture toughness: slow crack growth deflect crack tips redistribute stresses around crack tips bridge crack tips slow crack growth deflect crack tips redistribute stresses around crack tips bridge crack tips Matrix

17. Composites - polymer matrix composites (PMCs) Fibers: mainly - glass (GFRPs), carbon (CFRPs), aramid, others - B, SiC, Al 2 O 3 Fibers: mainly - glass (GFRPs), carbon (CFRPs), aramid, others - B, SiC, Al 2 O 3

18. Composites - polymer matrix composites (PMCs) Matrix

19. Composites - polymer matrix composites (PMCs) Very common - polyesters, vinyl esters

20. Composites Role of matrix in FR composites: a. transfer stresses betwn fibers b. provide barrier to environment c. protect fibers Role of matrix in FR composites: a. transfer stresses betwn fibers b. provide barrier to environment c. protect fibers Matrix/fiber bond: matrix must wet fiber physical & chemical bond desirable mechanical interlocking Matrix/fiber bond: matrix must wet fiber physical & chemical bond desirable mechanical interlocking Fibers frequently coated w/ coupling agent

21. non-coupled Composites coupled

22. Composites Fibers - variables amount fiber length distribution orientation Fibers - variables amount fiber length distribution orientation Fiber orientation can be random aligned intermediate Fiber orientation can be random aligned intermediate