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
Don’t always get what you want
Ex: combine ferret (pet) + mink (fur)
Desire a mink with good disposition but got a nasty ferret

3. Terminology/Classification
• Composites:
-- Multiphase material with significant
proportions of each phase.
woven
fibers
cross
section
view
0.5 mm
• 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

4. Matrix and Disperse phase of composites

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

7. Composite Survey: Particle-II
Particle-reinforced
Fiber-reinforced
Structural
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
threaded
rod
nut
Post tensioning – tighten nuts to put under tension

8. Composite Survey: Particle-III
Particle-reinforced
Fiber-reinforced
Structural
• Elastic modulus, Ec, of composites:
-- two approaches. c m
upper
limit: E = V + p
“rule of mixtures”
Data:
Cu matrix
w/tungsten
particles 20 4 6 8 10
150
250 30
350
vol% tungsten
E(GPa)
(Cu) ( W)
lower limit: 1 E c = V m + p
• 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
• 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.
matrix: a
(Mo) (ductile)
fibers: g
’ (Ni3Al) (brittle)
2 mm
(a)
(b)
fracture
surface

13. Composite Survey: Fiber-IV
Particle-reinforced
Fiber-reinforced
Structural
• 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.
(b)
fibers lie
in plane
view onto plane
C fibers:
very stiff
very
strong
C matrix:
less stiff
less strong
(a)
• Other variations:
-- Discontinuous, random 3D
-- Discontinuous, 1D

14. Composite Survey: Fiber-V
Particle-reinforced
Fiber-reinforced
Structural
• 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
• Why? Longer fibers carry stress more efficiently!
Shorter, thicker fiber:
Longer, thinner fiber:
Poorer fiber efficiency
Better fiber efficiency s
(x)

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 • Estimate of Ec and TS for discontinuous fibers:
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)
(TS)c = (TS)mVm + (TS)fVf
(aligned 1D)

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

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

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

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

27. PRICE AND AVAILABILITY
• Current Prices on the web: e.g.,
-- 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:
-- Energy to produce
materials (GJ/ton)
-- Cost of energy used in
processing materials ($/MBtu) Al
PET Cu
steel
glass
paper
237 (17)
103 (13)
97 (20) 20 13 9
elect resistance
propane
oil
natural gas 25 17 13 11
Energy prices from
Energy using recycled
material indicated in green.

28. RELATIVE COST, c, OF MATERIALS
Graphite/
Ceramics/
Semicond
Metals/
Alloys
Composites/
fibers
Polymers
Relative Cost (c)
pl. carbon Au
Si wafer
PET
Epoxy
Nylon 6,6
0.05
0.1 5
100000
10000 2
0000
000 1 00
0.5
Steel
high alloy
Al alloys Cu
alloys Mg Ti Ag Pt
Tungsten
Al oxide
Concrete
Diamond
Glass-soda
Si carbide
Si nitride PC
LDPE,HDPE PP PS
PVC
Aramid fibers
Carbon fibers
E-glass fibers
AFRE prepreg C
FRE prepreg G
Wood
• 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.

29. STIFF & LIGHT TENSION MEMBERS
F, d L 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)

30. STRONG & LIGHT TENSION MEMBERS
F, d L 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)

31. STRONG & LIGHT TORSION MEMBERS
• 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)

32. 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
tf (MPa)
1140
1060
300
525
780
P [(MPa)2/3m3/Mg] 73 52 16 15 11
• Lightest: Carbon fiber reinforced epoxy
(CFRE) member.

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

34. 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,