1. 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
Reprinted with permission from
D. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47. 2

3. COMPOSITE SURVEY: Particle-I
Particle-reinforced
• Examples:
Adapted from Fig , Callister 6e. (Fig is copyright United States Steel Corporation, 1971.)
Adapted from Fig. 16.4, Callister 6e. (Fig is courtesy Carboloy Systems, Department, General Electric Company.)
Adapted from Fig. 16.5, Callister 6e. (Fig is courtesy Goodyear Tire and Rubber Company.) 3

4. COMPOSITE SURVEY: Particle-II
Particle-reinforced
• Elastic modulus, Ec, of composites:
-- two approaches.
Adapted from Fig. 16.3, Callister 6e. (Fig is from R.H. Krock, ASTM Proc, Vol. 63, 1963.)
• 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)
From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig , p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRC
Press, Boca Raton, FL.
(b)
From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp , Used with permission. 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
Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p (Courtesy I.J. Davies) Reproduced with permission of CRC Press, Boca Raton, FL. 6

7. COMPOSITE SURVEY: Structural
• Stacked and bonded fiber-reinforced sheets
-- stacking sequence: e.g., 0/90
-- benefit: balanced, in-plane stiffness
Adapted from Fig , Callister 6e.
• Sandwich panels
-- low density, honeycomb core
-- benefit: small weight, large bending stiffness
Adapted from Fig ,
Callister 6e. (Fig is
from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987. 9

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9. Metal Matrix Composites

10. Key Properties for MMC
Al, Ti and Fe based composites are most common MMCs.
High strength
Light weight
High stiffness
High toughness
High electrical conductivity (e.g. Cu-Diamond)
High thermal conductivity

11. MMCs Two Components MMCs reinforcements could be
Metal Matrix and usually Ceramic reinforcement
MMCs reinforcements could be
Continuous/Discontinuous Fibers
Whiskers
wires
Particulates (Most Common)

12. Cont. Fiber are not used as reinforcement!
Due to exorbitant manufacturing costs associated with the high cost of fibers
Highly labor intensive manufacturing process
Damage to fiber during high temperature processing (liquid metal flow, handling etc.)
Particulates does good job- a wide spectrum of reinforcement could be used with conventional processing technique obviating the need for complex fiber winding machines
Homogenous and Isotropic material properties are obtained with substantial improvements in strength and stiffness than that of monolithic material.

13. Strength of MMC Depends On
Diameter of the reinforcing particle
The interparticle spacing
Volume fraction of the reinforcement
The condition at the particle/matrix interface
Work hardening coefficient of the matrix

14. Reinforcement Materials
Typical reinforcements are : SiC, B4C, Al2O3 ,Si3N4 and TiC particulates
B, C, Al2O3 , SiC, and W fibers
Al2O3 : most promising reinforcement at high temp. applications in chemically aggressive environment
Retains strength, stiffness, abrasion resistance and oxidation resistance up to 850 deg C
SiC is another important reinforcement with even higher temperature capabilities

15. Interface in MMCs Usually reinforcement are ceramic in MMC
Hence METAL/CERAMIC interface is most common and important to study
Interface is very important because
It occupies a large surface area in composites
It forms a system which is not in “thermodynamic equilibrium”
Interface is “bidimensional” region of “discontinuity”. There is always some “volume” over which a gradual transition in material property occurs.
The major discontinuities are:
Elastic modulus
Chemical potential and
Coefficient of thermal expansion (CTE)

16. Processing Techniques Chart

17. COMPOSITE BENEFITS • CMCs: Increased toughness • PMCs: Increased E/r
• MMCs:
Increased
creep
resistance
Adapted from T.G. Nieh, "Creep rupture of a silicon-carbide reinforced aluminum composite", Metall. Trans. A Vol. 15(1), pp , Used with permission. 10

18. 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