1. Registered Electrical & Mechanical Engineer BMayer@ChabotCollege.edu
Engineering 45
Composite Materials
Bruce Mayer, PE
Registered Electrical & Mechanical Engineer

2. Learning Goals – Composites
List The CLASSES and TYPES of Composites
When to Use Composites Instead of Metals, Ceramics, or Polymers
How to Estimate Composite Stiffness & Strength
Examine some Typical Applications

3. Terms & Classifications
Composite  MultiPhase Material with Significant Proportions of Each Phase
Phase Components
MATRIX
DISPERSED Phase
Matrix
The CONTINUOUS Phase
The Matrix Function
transfer stress to other phase(s)
Protect other phase(s) from the (corrosive) Environment
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.

4. Terms & Classifications cont.1
Composite Classifications
MMC  Metal Matrix Composite
CMC  Ceramic Matrix Comp.
PMC  Polymer Matrix Comp.
Dispersed Phase (DP)
Function = To Enhance the Matrix Properities
MMC: increase σy, TS/σu, creep resistance
CMC: increase Kc (fracture toughness)
PMC: increase E, σy, TS/σu, creep resistance
Classes: Particle, fiber, structural

5. DISPERSION Strengthened
Composite Taxonomy
Composites
PARTICLE Reinforced
FIBER Reinforced
STRUCTURAL
LARGE Particle
DISPERSION Strengthened
Continous (Aligned)
DIScontinous (Short)
Laminates
Sandwich Panels
Aligned
Randomly Oriented

6. Composite Survey – Particle-I
Particle-reinforced
Fiber
-reinforced
Structural
Examples 60
Adapted from Fig , Callister 7e. (Fig is copyright United States Steel Corporation, 1971.)
-Spheroidite
steel
matrix:
ferrite ( a )
(ductile)
particles:
cementite ( Fe 3 C
(brittle) m
Adapted from Fig. 16.4, Callister 7e. (Fig is courtesy Carboloy Systems, Department, General Electric Company.)
-WC/Co
cemented
carbide
matrix:
cobalt
(ductile)
particles: WC
(brittle,
hard) V m :
10-15vol%!
600
Adapted from Fig. 16.5, Callister 7e. (Fig is courtesy Goodyear Tire and Rubber Company.)
-Automobile
tires
matrix:
rubber
(compliant)
particles: C
(stiffer)
0.75 m

7. ReInforced ConCrete Concrete is a PARTICLE ReInforced Composite
Matrix = PortLand Cement
3CaO-SiO2 + 2CaO-SiO2
Dispersed Phases
Sand+Gravel Aggregate
60%-80% by Vol
Steel ReInforcing Bars (Rebar)
A type of FIBER Reinforcement
Improves Tensile & Shear Strength

8. More ReInforced Concrete
Concrete ≡ gravel + SAND + cement
Why sand and gravel? → Sand packs into gravel VOIDS
Reinforced concrete - Reinforce with steel reBAR or reMESH
Increases TENSILE strength - even if Concrete matrix is cracked
PreStressed concrete - reMesh under tension during setting of concrete. Tension release puts concrete under COMPRESSIVE Stress
Concrete is much stronger under compression.

9. Composite Survey – Particle-II
Particle-reinforced
Fiber
-reinforced
Structural
Composite Material Elastic Modulus, Ec
Two “Rule of Mixtures” Approximations
Data:
Cu matrix
w/tungsten
particles 20 4 6 8 10
150
250 30
350
vol% tungsten
E(GPa)
lower limit: 1 E c = V m + p
upper
limit:
(Cu) ( W)
“rule of mixtures”
←Springs in PARALLEL
Upper Limit is like Springs in PARALLEL: if Vm ~ Vp; then larger Ei dominates
Lower limit => Ec = EmEp/ (VmEp + VpEm) => Then smaller Ei dominates
←Springs in SERIES
Rule-of-Mixtures Applies to Other Properties
Electrical conductivity, σelect: Replace E by σelect
Thermal conductivity, k: Replace E by k.

10. Composite Survey: Fiber-I
Fibers very strong
Provide significant strength improvement compared to pure matrix-material
Example: fiber-glass
Continuous glass filaments in a polymer matrix
Strength due to fibers
Polymer simply holds them in place

11. Fiber Materials
Whiskers - Thin single crystals - large length to diameter ratio
graphite, SiN, SiC
high crystal perfection – extremely strong, strongest known
very expensive
Traditional Fibers
polycrystalline or amorphous
Generally polymers or ceramics
Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE
UltraHighMolecularWeightPolyEthylene

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

13. Fiber Alignment aligned continuous aligned random discontinuous
Adapted from Fig. 16.8, Callister 7e.
aligned
continuous
aligned random
discontinuous

14. ISOstress & ISOstrain
isoSTRAIN → Tensile strength and elastic modulus when fibers are parallel to the direction of stress
isoSTRESS → Tensile strength and elastic modulus when fibers are perpendicular to the direction of stress

15. Composite Survey – Fiber-I
Fiber-reinforced
Particle-reinforced
Structural
ALIGNED, CONTINUOUS Fibers
Examples
Metal: g’ (Ni3Al)-a(Mo)
by eutectic solidification.
From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp , Used with permission.
matrix: a
(Mo)
(ductile)
fibers: g’
(Ni 3
Al)
(brittle) 2 m
Glass w/SiC fibers
formed by glass slurry
Eglass = 76GPa; ESiC = 400GPa.
(a)
(b)
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.

16. Composite Survey – Fiber-II
Fiber-reinforced
Particle-reinforced
Structural
DISCONTINUOUS, RANDOM, 2D (Planer) Fibers
Example: Carbon-Carbon
Process: fiber/pitch, then burn out at up to 2500C.
Uses: disk brakes, gas turbine exhaust flaps, rocket nose cones.
Other variations:
Discontinuous, random 3D
Discontinuous, 1D
Fully Aligned
C fibers:
very stiff
very
strong
C matrix:
less stiff
less strong
(b)
view onto plane
fibers lie
in plane
(a)
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.

17. Composite Survey – Fiber-III
Fiber-reinforced
Particle-reinforced
Structural
CRITICAL fiber length for effective stiffening & strengthening:
fiber diameter
shear strength of
fiber-matrix interface
fiber strength in tension
The Equation Balances (want PullOut ≥ Tear)
The Fiber Load capacity → σf•[ACylXsec] = σf•[πd2/4]
The Fiber Pull-Out Force→ c•[ACylSurf] = c•[πd•l]
Stronger Fibers → need LONGER fiber
Stronger Fiber-Matrix Shear-Bond → need SHORTER Fiber

18. Fiber Lengths cont. Example: FiberGlass
Need Fiber Lengh > 15mm
Reason for length Criteria → examine Extreme cases
Very Short Fiber has very little hold-in force and would PULL-OUT (Fiber PULLS OUT before Fracture)
Very Long Fiber would take almost all the axial load (Fiber FRACTURES before PullOut)
Shorter, thicker fiber:
Longer, thinner fiber:
Poorer fiber efficiency
Better fiber efficiency
Adapted from Fig. 16.7, Callister 6e.

19. Composite Survey – Fiber-IV
Fiber-reinforced
Particle-reinforced
Structural
Typical Values for K:
Aligned 1D: K = 1 (anisotropic)
Random 2D: K = 3/8 2D isotropy)
Random 3D: K = 1/5 (3D isotropy)
TS in fiber direction (1D, Aligned) by VOLUME Weighted Average
Estimate Ec and TS
Valid for LONG Fiber Condition:
The Elastic Modulus in Fiber Direction
efficiency factor

20. Composite Survey – Structural
Fiber
-reinforced
Particle-reinforced
Stacked and bonded fiber-reinforced sheets
Orthogonal stacking sequence: e.g., 0°/90°
benefit: balanced, in-plane stiffness
Sandwich panels
low density, honeycomb core
benefit: small weight, large bending stiffness
honeycomb
adhesive layer
face sheet
Think PLYWOOD and LAMINATED BEAM tested in the Lab
Similar to Composite Beam Lab Exercise

21. Composite Benefits
Ceramic Matrix Composites → Better FRACTURE TOUGHNESS
Metal Matrix Composites → Improved CREEP RESISTANCE
fiber
-reinf
un-reinf
particle-reinf
Force
Bend
displacement

22. Composite Benefits cont.1
Polymer Matrix Composites → Better E:ρ (Stiffness:Weight) ratio
E(GPa)
G=3E8
K=E
Density, r
[Mg/m 3 ] .1 .3 1 10
.01 2
metal/
metal alloys
polymers
PMCs
ceramics
Want: HI Modulus; Lo density

23. Specific Strength
The PRIMARY Motivation for the Use of Composites → Hi-Strength, Hi-Stiffness & Lo-Weight
Thus Two Important Metrics
Specific STRENGTH
Similarly The Specific STIFFNESS
Now Specific Weight
Where
ρ  Density in kg/m3
g  Acceleration of Gravity (9.81 m/s2)

24. Specific Strength cont.1
Now Determine Units for Sσ and SE by Way of Examples
For 7075 Al in the Heat treated State
u = 83 ksi
 = lb/in3
For Kevlar-49 (Aramid Fiber)
E = 131 GPa
ρ = 1444 kg/m3
Find 
Now Specific Stiffness

26. Sσ vs SE Comparison The High DENSITY of Metal Reduces Sσ and SE
The Low STRENGTH & STIFFNESS of most Polymers Reduces Sσ and SE

27. Summary – Composite Matls
Composites Classified by:
The Matrix Material
Ceramic (CMC)
Metal (MMC)
PolyMer (PMC)
ReInforcement Geometry
Particles
Fibers
Layers

28. Summary – Composites cont.1
Composites enhance matrix properties:
MMC: enhance sy, TS, creep performance
CMC: enhance Kc
PMC: enhance E, sy, TS, creep resistance
Particle ReInforced
Elastic modulus can be estimated by the Rule of Mixtures
Properties are isotropic

29. Summary – Composites cont.2
Fiber ReInforced:
Elastic modulus and TS can be estimated along fiber direction By Rule of Mixtures
Properties can be isotropic or anisotropic
Structural:
Based on build-up of sandwiches in layered form
Plys
HoneyCombs

30. WhiteBoard Work Prob 16.11 Where
Given IsoStrain, Longitudinal Loading for a Continuous Fiber Composite:
Where
F  Force
E  Elastic Modulus
V  Volume fraction
Sub-f → “fiber”
Sub-m → “matrix”
Sub-c → “composite”
Then Show

31. Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu
Chabot Engineering
Appendix E-glass
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer

32. E Glass - BackGround http://www.azom.com/details.asp?ArticleID=764
E-Glass or electrical grade glass was originally developed for stand off insulators for electrical wiring. It was later found to have excellent fibre forming capabilities and is now used almost exclusively as the reinforcing phase in the material commonly known as fibreglass.

33. E Glass - Composition Composition
E-Glass is a low alkali glass with a typical nominal composition of SiO2 54wt%, Al2O3 14wt%, CaO+MgO 22wt%, B2O3 10wt% and Na2O+K2O less then 2wt%. Some other materials may also be present at impurity levels.

34. E Glass – Key Properties
Properties that have made E-glass so popular in fibreglass and other glass fibre reinforced composite include:
Low cost
High production rates
High strength, (see table on next slide)
High stiffness
Relatively low density
Non-flammable
Resistant to heat
Good chemical resistance
Relatively insensitive to moisture
Able to maintain strength properties over a wide range of conditions
Good electrical insulation

35. E Glass – Fibre Strength
Table 1. Comparison of typical properties for some common fibres.

36. E Glass – Use in Composites
The use of E-Glass as the reinforcement material in polymer matrix composites is extremely common. Optimal strength properties are gained when straight, continuous fibres are aligned parallel in a single direction. To promote strength in other directions, laminate structures can be constructed, with continuous fibres aligned in other directions. Such structures are used in storage tanks and the like.
Random direction matts and woven fabrics are also commonly used for the production of composite panels, surfboards and other similar devices.