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Creep

Creep. Relaxation. Creep of cellulose acetate. 40 0 C. 10. 60 0 C. 92 0 C. 80 0 C. 100 0 C. 9. Log E(t), (dynes/cm 2 ). 110 0 C. Stress relaxation. of PMMA. 112 0 C. 8. 120 0 C. 115 0 C. 125 0 C. 7. 135 0 C. 0.001. 0.01. 0.1. 1. 10. 100. 1000. Time (hours).

robin-hooper
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Creep

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  1. Creep Relaxation

  2. Creep of cellulose acetate

  3. 400C 10 600C 920C 800C 1000C 9 Log E(t), (dynes/cm2) 1100C Stress relaxation of PMMA 1120C 8 1200C 1150C 1250C 7 1350C 0.001 0.01 0.1 1 10 100 1000 Time (hours) Relaxation in PMMA

  4. Creep & recovery

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

  6. H H – – Polyvinyl chloride (PVC) {-C-C-}n – – Cl H Some specific polymers 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. Some specific polymers silicones Oils - Low MW……liquids lubricants, hydraulic fluids, water repellants, usw. Elastomers - intermediate MW, crosslinked waterproofing, caulk, prostheses, 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

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

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

  11. H2C-C-C{-O- -C- -O-}nC-C-CH2 H H H H-C-H H-C-H O O H H H H2N-R-NH2 hardener epoxy Prepregs Some specific polymers

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

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

  14. Works like precipitation hardening Composites - metal matrix composites (MMCs) Particulates: ThO2-dispersed Ni (TD Ni) sintered Al powder (SAP) - except strengthening maintained at hi T Improves: strength creep resistance hi T corrosion resistance

  15. Matrix mat'ls Composites - metal matrix composites (MMCs) Fibers: Conts - C, SiC, B, Al2O3 Disconts - C, Al2O3 , SiC whiskers May get rxn betwn phases at hi T

  16. Matrix Composites - ceramic matrix composites (CMCs) Particulates, fibers: SiC, B, Al2O3 , C, SiC & Si3N4 whiskers Improve fracture toughness: slow crack growth deflect crack tips redistribute stresses around crack tips bridge crack tips

  17. Composites - polymer matrix composites (PMCs) Fibers: mainly - glass (GFRPs), carbon (CFRPs), aramid, others - B, SiC, Al2O3

  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 Matrix/fiber bond: matrix must wet fiber physical & chemical bond desirable mechanical interlocking Fibers frequently coated w/ coupling agent

  21. non-coupled coupled Composites

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

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