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Chapter 16: Composite Materials

Chapter 16: Composite Materials. ISSUES TO ADDRESS. • What are the classes and types of composites ?. • Why are composites used instead of metals, ceramics, or polymers?. • How do we estimate composite stiffness & strength?. • What are some typical applications?. Composites.

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Chapter 16: Composite Materials

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  1. Chapter 16: Composite Materials ISSUES TO ADDRESS... • What are the classes and types of composites? • Why are composites used instead of metals, ceramics, or polymers? • How do we estimate composite stiffness & strength? • What are some typical applications?

  2. Composites • Combine materials with the objective of getting a more desirable combination of properties • Ex: get flexibility & weight of a polymer plus the strength of a ceramic • Principle of combined action • Mixture gives “averaged” properties

  3. Terminology/Classification woven fibers • Matrix: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment -- Classification: MMC, CMC, PMC 0.5 mm cross section view metal ceramic polymer 0.5 mm • Composites: -- Multiphase material with significant proportions of each phase. • Dispersed phase: -- Purpose: enhance matrix properties. MMC: increase sy, TS, creep resist. CMC: increase Kc PMC: increase E, sy, TS, creep resist. -- Classification: Particle, fiber, structural

  4. Matrix and Disperse phase of composites

  5. Composite Survey Composites Fiber-reinforced Particle- reinforced Structural Large- Dispersion- Continuous Discontinuous Sandwich Laminates particle strengthened (aligned) (short) panels Randomly Aligned oriented

  6. Composite Survey: Particle-I Particle-reinforced Fiber-reinforced Structural • Examples: particles: - Spheroidite matrix: cementite ferrite (a) steel ( Fe C ) (ductile) 3 (brittle) 60mm - WC/Co matrix: particles: cobalt WC cemented (ductile) (brittle, carbide hard) V : m 10-15 vol%! 600mm - Automobile matrix: particles: rubber tires C (compliant) (stiffer) 0.75mm

  7. Composite Survey: Particle-II Particle-reinforced Fiber-reinforced Structural Post tensioning– tighten nuts to put under tension threaded rod nut • Concrete– gravel + sand + cement • - Why sand and gravel? Sand packs into gravel voids • Reinforced concrete - Reinforce with steel rerod or remesh • - increases strength - even if cement matrix is cracked • Prestressed concrete - remesh under tension during setting of concrete. Tension release puts concrete under compressive force • - Concrete much stronger under compression. • - Applied tension must exceed compressive force

  8. Composite Survey: Particle-III Particle-reinforced Fiber-reinforced Structural upper limit: “rule of mixtures” = + E V E V E c m m p p E(GPa) 350 Data: lower limit: 30 0 Cu matrix V 1 V m p w/tungsten 250 = + E E E particles 20 0 c m p 150 vol% tungsten 0 20 4 0 6 0 8 0 10 0 (Cu) ( W) • Elastic modulus, Ec, of composites: -- two approaches. • Application to other properties: -- Electrical conductivity, se: Replace E in equations with se. -- Thermal conductivity, k: Replace E in equations with k.

  9. Composite Survey: Fiber-I Particle-reinforced Fiber-reinforced Structural • Fibers very strong • Provide significant strength improvement to material • Ex: fiber-glass • Continuous glass filaments in a polymer matrix • Strength due to fibers • Polymer simply holds them in place

  10. Composite Survey: Fiber-II Particle-reinforced Fiber-reinforced Structural • Fiber Materials • Whiskers - Thin single crystals - large length to diameter ratio • graphite, SiN, SiC • high crystal perfection – extremely strong, strongest known • very expensive • Fibers • polycrystalline or amorphous • generally polymers or ceramics • Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE • Wires • Metal – steel, Mo, W

  11. Fiber Alignment aligned continuous aligned random discontinuous

  12. Composite Survey: Fiber-III Particle-reinforced Fiber-reinforced Structural a matrix: (Mo) (ductile) (a) fracture surface 2mm g fibers: ’ (Ni3Al) (brittle) (b) • Aligned Continuous fibers • Examples: -- Metal: g'(Ni3Al)-a(Mo) by eutectic solidification. -- Ceramic: Glass w/SiC fibers formed by glass slurry Eglass = 76 GPa; ESiC = 400 GPa.

  13. Composite Survey: Fiber-IV Particle-reinforced Fiber-reinforced Structural C fibers: very stiff very strong (b) C matrix: less stiff view onto plane less strong fibers lie in plane (a) • Discontinuous, random 2D fibers • Example: Carbon-Carbon -- process: fiber/pitch, then burn out at up to 2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, nose cones. • Other variations: -- Discontinuous, random 3D -- Discontinuous, 1D

  14. Composite Survey: Fiber-V Particle-reinforced Fiber-reinforced Structural • Why? Longer fibers carry stress more efficiently! Shorter, thicker fiber: Longer, thinner fiber: s (x) s (x) Better fiber efficiency Poorer fiber efficiency • Critical fiber length for effective stiffening & strengthening: fiber strength in tension fiber diameter shear strength of fiber-matrix interface • Ex: For fiberglass, fiber length > 15 mm needed

  15. Composite Strength:Longitudinal Loading Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix • Longitudinal deformation c = mVm+ fVf but c= m= f volume fraction isostrain • Ece= Em Vm + EfVf longitudinal (extensional) modulus f = fiber m = matrix

  16. Composite Strength:Transverse Loading • In transverse loading the fibers carry less of the load - isostress c= m= f=  c= mVm+ fVf  transverse modulus

  17. Composite Strength Particle-reinforced Fiber-reinforced Structural • Estimate of Ec and TS for discontinuous fibers: -- valid when -- Elastic modulus in fiber direction: -- TS in fiber direction: Ec= EmVm + KEfVf efficiency factor: -- aligned 1D: K = 1 (aligned ) -- aligned 1D: K = 0 (aligned ) -- random 2D: K = 3/8 (2D isotropy) -- random 3D: K = 1/5 (3D isotropy) (aligned 1D) (TS)c= (TS)mVm + (TS)fVf

  18. Composite Production Methods-I • Pultrusion • Continuous fibers pulled through resin tank, then preforming die & oven to cure

  19. Composite Production Methods-II • Filament Winding • Ex: pressure tanks • Continuous filaments wound onto mandrel

  20. Composite Survey: Structural Particle-reinforced Fiber-reinforced Structural • Sandwich panels -- low density, honeycomb core -- benefit: small weight, large bending stiffness face sheet adhesive layer honeycomb • Stacked and bonded fiber-reinforced sheets -- stacking sequence: e.g., 0º/90º -- benefit: balanced, in-plane stiffness

  21. Composite Benefits • PMCs: Increased E/r ceramics Force 3 10 particle-reinf E(GPa) PMCs 2 10 10 metal/ fiber-reinf metal alloys 1 un-reinf .1 polymers G=3E/8 K=E .01 Bend displacement .1 .3 1 3 30 10 Density, r [mg/m3] -4 10 6061 Al e (s-1) ss • MMCs: Increased creep resistance -6 10 -8 6061 Al 10 w/SiC whiskers s (MPa) -10 10 20 30 50 100 200 • CMCs: Increased toughness

  22. Summary • Composites are classified according to: -- the matrix material (CMC, MMC, PMC) -- the reinforcement geometry (particles, fibers, layers). • Composites enhance matrix properties: -- MMC: enhance sy, TS, creep performance -- CMC: enhance Kc -- PMC: enhance E, sy, TS, creep performance • Particulate-reinforced: -- Elastic modulus can be estimated. -- Properties are isotropic. • Fiber-reinforced: -- Elastic modulus and TS can be estimated along fiber dir. -- Properties can be isotropic or anisotropic. • Structural: -- Based on build-up of sandwiches in layered form.

  23. Material Selection

  24. Material Classification

  25. The Materials Selection Process Processes Structure Shape Composition Mechanical Electrical Thermal Optical Etc. Materials Properties Environment Load Applications Functions

  26. PRICE AND AVAILABILITY • Current Prices on the web: e.g.,http://www.metalprices.com -- Short term trends: fluctuations due to supply/demand. -- Long term trend: prices will increase as rich deposits are depleted. • Materials require energy to process them: -- Cost of energy used in processing materials ($/MBtu) -- Energy to produce materials (GJ/ton) 237 (17) 103 (13) 97 (20) 20 13 9 Al PET Cu steel glass paper elect resistance propane oil natural gas 25 17 13 11 Energy using recycled material indicated in green.

  27. Graphite/ Metals/ Composites/ Ceramics/ Polymers Alloys fibers Semicond 100000 5 0000 Diamond 2 0000 Pt Au 10000 5 000 Si wafer 2 000 1 000 Si nitride 5 00 Ag alloys 2 00 C FRE prepreg Tungsten 1 00 AFRE prepreg Ti alloys Relative Cost (c) Si carbide Carbon fibers 5 0 Aramid fibers G FRE prepreg 2 0 Cu alloys Al alloys Nylon 6,6 1 0 Al oxide Mg alloys PC 5 Epoxy E-glass fibers high alloy PET Glass-soda PVC 2 LDPE,HDPE Steel Wood PP 1 PS pl. carbon 0.5 0.1 Concrete 0.05 RELATIVE COST, c, OF MATERIALS • Reference material: -- Rolled A36 plain carbon steel. • Relative cost, , fluctuates less over time than actual cost. Based on data in Appendix C, Callister, 7e. AFRE, GFRE, & CFRE = Aramid, Glass, & Carbon fiber reinforced epoxy composites.

  28. STIFF & LIGHT TENSION MEMBERS F, d L c c • Bar must not lengthen by more than d under force F; must have initial length L. -- Stiffness relation: -- Mass of bar: (s = Ee) • Eliminate the "free" design parameter, c: minimize for small M specified by application • Maximize the Performance Index: (stiff, light tension members)

  29. STRONG & LIGHT TENSION MEMBERS F, d L c c • Bar must carry a force F without failing; must have initial length L. -- Strength relation: -- Mass of bar: • Eliminate the "free" design parameter, c: minimize for small M specified by application • Maximize the Performance Index: (strong, light tension members)

  30. STRONG & LIGHT TORSION MEMBERS M t L t t 2R • Bar must carry a moment, Mt ; must have a length L. -- Strength relation: -- Mass of bar: • Eliminate the "free" design parameter, R: specified by application minimize for small M • Maximize the Performance Index: (strong, light torsion members)

  31. DETAILED STUDY I: STRONG, LIGHT TORSION MEMBERS • Maximize the Performance Index: • Other factors: --require sf > 300 MPa. --Rule out ceramics and glasses: KIc too small. • Numerical Data: material CFRE (vf= 0.65) GFRE (vf= 0.65) Al alloy (2024-T6) Ti alloy (Ti-6Al-4V) 4340 steel (oil quench & temper) r (Mg/m3) 1.5 2.0 2.8 4.4 7.8 P [(MPa)2/3m3/Mg] 73 52 16 15 11 tf (MPa) 1140 1060 300 525 780 • Lightest: Carbon fiber reinforced epoxy (CFRE) member.

  32. DETAILED STUDY II: STRONG, LOW COST TORSION MEMBERS cost/mass of material cost/mass of low-carbon steel • Numerical Data: (/P)x100 112 76 93 748 46 material CFRE (vf= 0.65) GFRE (vf= 0.65) Al alloy (2024-T6) Ti alloy (Ti-6Al-4V) 4340 steel (oil quench & temper) P [(MPa)2/3m3/Mg] 73 52 16 15 11 80 40 15 110 5 • Minimize Cost: Cost Index ~ M ~ /P(since M ~ 1/P) where M = mass of material = relative cost = • Lowest cost: 4340 steel (oil quench & temper) • Need to consider machining, joining costs also.

  33. SUMMARY • Material costs fluctuate but rise over the long term as: -- rich deposits are depleted, -- energy costs increase. • Recycled materials reduce energy use significantly. • Materials are selected based on: -- performance or cost indices. • Examples: -- design of minimum mass, maximum strength of: • shafts under torsion, • bars under tension, • plates under bending,

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