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CHAPTER 15: COMPOSITE MATERIALS

CHAPTER 15: 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?. 1.

sarah-mcknight
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CHAPTER 15: COMPOSITE MATERIALS

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  1. CHAPTER 15: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? 1

  2. TERMINOLOGY/CLASSIFICATION • Composites: --Multiphase material w/significant proportions of ea. phase. • Matrix: --The continuous phase --Purpose is to: transfer stress to other phases protect phases from environment --Classification: MMC, CMC, PMC metal ceramic polymer • 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 2

  3. COMPOSITE SURVEY: Particle-I Particle-reinforced • Examples: 3

  4. COMPOSITE SURVEY: Particle-II Particle-reinforced • Elastic modulus, Ec, of composites: -- two approaches. • Application to other properties: -- Electrical conductivity, se: Replace E by se. -- Thermal conductivity, k: Replace E by k. 4

  5. COMPOSITE SURVEY: Fiber-I Fiber-reinforced • Aligned Continuous fibers • Examples: --Metal: g'(Ni3Al)-a(Mo) by eutectic solidification. --Glass w/SiC fibers formed by glass slurry Eglass = 76GPa; ESiC = 400GPa. (a) (b) 5

  6. COMPOSITE SURVEY: Fiber-II Fiber-reinforced • Discontinuous, random 2D fibers • Example: Carbon-Carbon --process: fiber/pitch, then burn out at up to 2500C. --uses: disk brakes, gas turbine exhaust flaps, nose cones. (b) (a) • Other variations: --Discontinuous, random 3D --Discontinuous, 1D 6

  7. COMPOSITE SURVEY: Fiber-III Fiber-reinforced • Critical fiber length for effective stiffening & strengthening: fiber strength in tension fiber diameter shear strength of fiber-matrix interface • Ex: For fiberglass, fiber length > 15mm needed • Why? Longer fibers carry stress more efficiently! Shorter, thicker fiber: Longer, thinner fiber: Better fiber efficiency Poorer fiber efficiency 7

  8. COMPOSITE SURVEY: Fiber-IV Fiber-reinforced • Estimate of Ec and TS: --valid when -- Elastic modulus in fiber direction: --TS in fiber direction: efficiency factor: --aligned 1D: K = 1 (anisotropic) --random 2D: K = 3/8 (2D isotropy) --random 3D: K = 1/5 (3D isotropy) (aligned 1D) 8

  9. COMPOSITE SURVEY: Structural Structural • Stacked and bonded fiber-reinforced sheets -- stacking sequence: e.g., 0/90 -- benefit: balanced, in-plane stiffness • Sandwich panels -- low density, honeycomb core -- benefit: small weight, large bending stiffness 9

  10. COMPOSITE BENEFITS • CMCs: Increased toughness • PMCs: Increased E/r • MMCs: Increased creep resistance 10

  11. 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. 11

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