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comp.ppt
1. Chapter 16-
ISSUES TO ADDRESS...
• What are the classes and types of composites?
1
• Why are composites used instead of metals,
ceramics, or polymers?
• How do we estimate composite stiffness & strength?
• What are some typical applications?
CHAPTER 16:
COMPOSITE MATERIALS
2. Chapter 16-
Definition of Composite Materials
• It contains two or more physically distinct and
mechanically separable materials
• It is made by dispersing one material in the other in a
controlled way to achieve optimum properties
• The properties of the composite are superior and
possibly unique in some specific respects to the
properties of individual components
Professor Derek Hull
University of Liverpool
3. Chapter 16- 2
• 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
• 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
metal ceramic polymer
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.
TERMINOLOGY/CLASSIFICATION
4. Chapter 16- 3
Particle-reinforced
• Examples:
Adapted from Fig.
10.10, Callister 6e.
(Fig. 10.10 is
copyright United
States Steel
Corporation, 1971.)
Adapted from Fig.
16.4, Callister 6e.
(Fig. 16.4 is courtesy
Carboloy Systems,
Department, General
Electric Company.)
Adapted from Fig.
16.5, Callister 6e.
(Fig. 16.5 is courtesy
Goodyear Tire and
Rubber Company.)
COMPOSITE SURVEY: Particle-I
5. Chapter 16- 4
• 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.
Particle-reinforced
Adapted from Fig. 16.3,
Callister 6e. (Fig. 16.3 is
from R.H. Krock, ASTM
Proc, Vol. 63, 1963.)
COMPOSITE SURVEY: Particle-II
8. Chapter 16-
Basic Principles of Reinforcement
• Types of reinforcing elements
• Forms of reinforcing elements
• Direction of reinforcement
• Load transferring ability
• Volume fraction of reinforcements
• Continuous vs. discontinuous reinforcement
9. Chapter 16-
Characteristics of fiber-reinforced Composites
• Amount of fibers
• Orientation of fibers
• Types of fibers
• Fiber aspect ratio
• Fiber orientation effects
• Strain rate effects
• Type of matrix
• Interfacial bonding conditions
11. Chapter 16-
Glass Fibers
• Glass is an amorphous material that consists of a silica
(SiO2) backbone with various oxide components to
give specific compositions and properties.
• Types: E-glass, S-glass, C-glass, quartz
• E-glass: calcium aluminoborosilicate with 2% alkali;
good strength and electrical resistivity; the least
expensive one
• S-glass: 40% higher than E-glass; high temp
application
• C-glass: soda limeborosilicate; use in corrosive
environments
• Quartz: low dielectric; use for protecting antennas and
radomes
14. Chapter 16-
Use of Glass Fibers
• Tensile strength is highly dependent on surface
defects. The shorter the sample, the higher the value.
• Moisture has a detrimental effect on strengths
• Temperature has profound impact on strength and
modulus. The higher the temperature, the lower the
strength (E-glass will be lower than S-glass). The
higher the temperature, the higher the tensile modulus
(E and S are about the same)
15. Chapter 16-
Surface Treatments
• Glass fibers are very brittle and susceptible
to developing tiny cracks when processed
lead to premature failure
• Sizing effect – a thin temporary water
soluble coating
• Coupling agent – Silanes
17. Chapter 16-
Carbon/Graphite Fibers
• Three precursors: polyacrylonitrile (PAN),
Rayon, and mesophase pitch fibers, stretched
and heated at 350o
C then 1000o
C
• CVD method: Pyrolytic deposition (via
methane, benzene and naphthalene) at 1000o
C
• Carbon fibers heated to 2000o
C with/without
stretching (graphitization) graphite fibers
21. Chapter 16-
Organic Fibers
• Para-phenylene diamine and terephthaloyl chloride are mixed in
an organic solvent to form poly paraphenyleneterephthalamide.
• Developed from aromatic polyamides, also known as aramid
fibers
• Manufactured by E.I. Du Pont with a trade name – Kevlar
• It is fully aligned and closely packed
• The polymer is washed and then dissolved in sulfuric acid. 20
wt% polymer solution is then passed through an extruder and
spinnerettes to develop a high degree of orientation (liquid crystal
form; process patented)
• Four types of aramid fibers: kevlar®, Kevlar 29 (high toughness),
kevlar 49 (high modulus) and kevlar 149 (ultra-high modulus)
• Kevlar fibers are less brittle than carbon or glass fibers, however, a
combination of good strength, light weight and excellent
toughness has led to the unique applications for aramid composites
25. Chapter 16-
Inorganic Fibers
• A class of short crystalline fibers, often called crystal
whisker fibers
• Made of aluminum oxide, beryllium oxide, magnesium
oxide, potassium titanate, silicon carbide, silicon nitride,
titanium boride, etc.
• Boron and silicon carbide fibers are popular because
they offer very high tensile strength and modulus.
• Boron fibers are considered amorphous (crystal structure
is small), but SiC has a much larger crystal structure.
• Boron fibers have a surface structure like scale or
corncob appearance. SiC fibers have a smoother surface
than boron.
• Boron composites have excellent tensile property
retention with increasing temperature
26. Chapter 16-
Boron/Silicon Carbide
• Boron trichloride interacts with the tungsten filament to form
tungsten borides, simultaneous bonded with the deposited boron
coated layers.
• Silicon carbide, a structure similar to diamond, offers a low
density, high stiffness, high strength and excellent thermal
stability and thermal conductivity properties.
• Growth from a melt --whisker form – defect free, single crystal
rod, 0.1-1μm in diameter
• CVD on fine carbon (30 μm) or tungsten (10 μm) fiber core to
yield a large-diameter SiC monofilament fiber (100-150 μm)
• Developed from polycarbosilane (PCS) precursor, stretched and
heated at 1300oC .
28. Chapter 16-
Properties of Boron and SiC Filaments
Boron Silicon Carbide
Density (g/cc) 2.40-2.59 2.98-3.20
Tensile Strength
(GPa)
3.60 3.90
Tensile Modulus
(GPa)
441 400
Elongation (%) 0.9 N/A
CTE (10-6
cm/cm/o
C)
2.5 N/A
Cost ($/lb) 320 100
29. Chapter 16-
Thermal Stability of Fibers
• Carbon fibers can be used in high temperatures (above
2000o
C) in which the oxidizing environments are
absent.
• The strength and modulus of silica based glass fibers
decrease rapidly above 250o
C and have a softening
point around 850o
C. Aramid fibers are worse than
carbon and glass fibers at high temperatures. Aramid
fibers can be attacked by UV lights as well.
• Inorganic fibers (Al2O3 and SiC) can sustain much
higher temperatures (above 2500o
C)
30. Chapter 16-
Flexibility
• The flexibility of a fiber, defined as k/M,
can be expressed in moment, M.
• Where E is the tensile modulus, d is the
fiber diameter and k is the reciprocal of the
radius of the curvature
35. Chapter 16-
The Rule of Mixtures
• Density
c= Vmm +Vf f
• Thermal Conductivity
Kc= Vm Km+Vf Kf
• Electrical Conductivity
sc= Vmsm+Vf sf
36. Chapter 16-
Modulus of Elasticity (iso-strain)
• When a stress is applied parallel to the fiber
orientation direction, the modulus of the
elasticity of the composite can be expressed
as
Ec= Vm Em+Vf Ef (to be derived later)
Since the matrix contributes little to the
stiffness of the composite, the modulus can
be simplified as
Ec =Vf Ef
37. Chapter 16-
Modulus of Elasticity (iso-stress)
• When a stress is applied perpendicular to
the fiber orientation direction
• The modulus of the composite is expressed
as
f
f
m
m
c E
V
E
V
E
1
38. Chapter 16-
Iso-Strain Loading
Force is applied along the axis of the fibers
The total force is the sum of all forces carried by
matrix and fibers
Fc = Fm +Ff
Since F =sA, scAc= smAm+ sfAf
sc =smVm+sfVf (assuming uniform cross-section,
area fraction is the same as volume fraction)
Iso-strain condition, c = f = m
Ec=VmEm+VfEf
)
A
A
(
)
A
A
(
c
f
f
c
m
m
c s
s
s
39. Chapter 16-
Iso-Stress Loading
• Force is vertically applied to the axis of the fibers
(the strains are no longer equal – each component
acts independently)
• c=Vmm+Vff
Since sc=sm=sf
The modulus of the elasticity of the composite is
now expressed as
)
E
(
)
E
(
E f
f
f
m
m
m
c
c
V
V
s
s
s
)
E
1
(
V
)
E
1
(
V
E
1
f
f
m
m
c
40. Chapter 16-
Example 1
Boron fibers (40 v%) are used to reinforce
aluminum for an engineering application. Use the
table provided below to calculate the density,
modulus of elasticity, and tensile strength long the
fiber orientation. Also estimate the modulus of
elasticity if the load is to be applied perpendicular
to the fibers.
Material Density (g/cc) Modulus
(ksi)
UTS
(ksi)
Fibers 2.36 55,000 400
Aluminum 2.70 10,000 5
41. Chapter 16-
From the rule of mixture
For density:
c= Vmm +Vf f
c= (0.6) (2.7)+(0.4) (2.36) = 2.56 g/cc
For modulus:
Ec= Vm Em+Vf Ef
Ec= (0.6) (10 x 106) +(0.4) (55 x 106)= 28 x 106 psi
For tensile strength:
UTS = (0.6) (5,000) +(0.4) (400,000) = 163,000 psi
Loading perpendicular to fibers:
psi
10
9
.
14
E
1
10
06727
.
0
10
55
4
.
0
10
10
6
.
0
E
V
E
V
E
1
6
6
6
6
x
x
x
x
c
f
f
m
m
c
42. Chapter 16-
Example 2
E-glass fibers are used to reinforce nylon in
an industrial application. If the nylon
contains 30 vol% glass fibers, what fraction
of the applied force is carried by the glass
fibers? (The modulus of elasticity for E-
glass fibers and nylon are 10.5 x106 psi and
0.4 x106 psi, respectively)
43. Chapter 16-
Assume equal strain (iso-strain) condition
Why? If the bonding is good, the composite should
yield only one strain value.
c = f = m
%
92
918
.
0
7
.
0
)
25
.
26
/
1
(
)
3
.
0
(
3
.
0
)
7
.
0
)(
/
(
)
3
.
0
(
3
.
0
by
divided
then
is
fraction
The
)
7
.
0
(
)
3
.
0
(
)
3
.
0
(
A
A
A
F
F
F
fraction
Force
25
.
26
10
4
.
0
10
5
.
10
E
E
E
E
E
E
6
6
f
m
f
m
f
f
m
m
f
f
f
f
m
f
f
f
m
m
f
f
f
m
m
f
f
f
m
m
m
psi
x
psi
x
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
44. Chapter 16-
How about particle reinforcement?
• The formula will have to be modified.
• Kc is an empirical constant. If its value is smaller
than one, then the equal (iso) strain condition can’t
be applied.
• Kc and Ks are different constants, both are
determined in the lab
p
p
c
m
m
c E
V
K
E
V
E
p
p
s
m
m
c TS
V
K
TS
V
TS )
(
)
(
45. Chapter 16-
Deformation Mechanisms in Composites
Parallel to fiber orientation:
• Stage I: Strain is small, fibers and matrix both elongate
(or deform) elastically
Fibers carry the load, EcVfEf
• Stage II: Incompatibility of the lateral matrix and fiber
deformation strains
Matrix deforms plastically; Fibers deform
elastically
• Stage III: Fiber deformed plastically before fracture
(found in metallic fibers)
Both matrix and fibers deform plastically
46. Chapter 16-
Reinforcement with Discontinuous Fibers
• Fiber midpoint offers the lowest shear stress
and highest highest tensile stress
• Fibers have to reach a critical aspect ratio
(lc/df), equal strain condition
my
c
f
f
c
d
l
s
2
)
(
c
c
m
m
c
c
f
f
c
c
c
c
m
m
c
c
f
f
c
c
l
l
V
l
l
V
l
l
V
l
l
V
when
)
(
2
)
(
)
(
when
)
(
]
2
1
)[
(
)
(
s
s
s
s
s
s
47. Chapter 16-
Characteristics of fiber-reinforced Composites
• Amount of fibers
• Orientation of fibers
• Types of fibers
• Fiber aspect ratio
• Fiber orientation effects
• Strain rate effects
• Type of matrix
• Interfacial bonding conditions
48. Chapter 16- 5
• Aligned Continuous fibers
Fiber-reinforced
Particle-reinforced Structural
• Examples:
From W. Funk and E. Blank, “Creep
deformation of Ni3Al-Mo in-situ
composites", Metall. Trans. A Vol. 19(4), pp.
987-998, 1988. Used with permission.
--Metal: g'(Ni3Al)-a(Mo)
by eutectic solidification.
--Glass w/SiC fibers
formed by glass slurry
Eglass = 76GPa; ESiC = 400GPa.
From F.L. Matthews and R.L.
Rawlings, Composite Materials;
Engineering and Science, Reprint
ed., CRC Press, Boca Raton, FL,
2000. (a) Fig. 4.22, p. 145 (photo by
J. Davies); (b) Fig. 11.20, p. 349
(micrograph by H.S. Kim, P.S.
Rodgers, and R.D. Rawlings). Used
with permission of CRC
Press, Boca Raton, FL.
(a)
(b)
COMPOSITE SURVEY: Fiber-I
49. Chapter 16- 6
• Discontinuous, random 2D fibers
Fiber-reinforced
Particle-reinforced Structural
• Example: Carbon-Carbon
--process: fiber/pitch, then
burn out at up to 2500C.
--uses: disk brakes, gas
turbine exhaust flaps, nose
cones.
• Other variations:
--Discontinuous, random 3D
--Discontinuous, 1D
fibers lie
in plane
view onto plane
C fibers:
very stiff
very strong
C matrix:
less stiff
less strong
Adapted from F.L. Matthews and R.L. Rawlings,
Composite Materials; Engineering and Science,
Reprint ed., CRC Press, Boca Raton, FL, 2000.
(a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151.
(Courtesy I.J. Davies) Reproduced with
permission of CRC Press, Boca Raton, FL.
(b)
(a)
COMPOSITE SURVEY: Fiber-II
50. Chapter 16- 7
• Critical fiber length for effective stiffening & strengthening:
Fiber-reinforced
Particle-reinforced Structural
fiber length 15
sf d
c
fiber diameter
shear strength of
fiber-matrix interface
fiber strength in tension
• Ex: For fiberglass, fiber length > 15mm needed
• Why? Longer fibers carry stress more efficiently!
fiber length 15
sf d
c
Shorter, thicker fiber:
fiber length 15
sf d
c
Longer, thinner fiber:
Poorer fiber efficiency Better fiber efficiency
Adapted from Fig.
16.7, Callister 6e.
COMPOSITE SURVEY: Fiber-III
51. Chapter 16-
• 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)
8
Fiber-reinforced
Particle-reinforced Structural
fiber length 15
sf d
c
Ec EmVm KEf Vf
(TS)c (TS)m Vm (TS)f Vf (aligned 1D)
Values from Table 16.3, Callister 6e.
(Source for Table 16.3 is H. Krenchel,
Fibre Reinforcement, Copenhagen:
Akademisk Forlag, 1964.)
COMPOSITE SURVEY: Fiber-IV
52. Chapter 16- 9
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
Adapted from
Fig. 16.16,
Callister 6e.
Adapted from Fig. 16.17,
Callister 6e. (Fig. 16.17 is
from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.
COMPOSITE SURVEY: Structural
53. Chapter 16- 10
• CMCs: Increased toughness • PMCs: Increased E/
• 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.
139-146, 1984. Used with permission.
COMPOSITE BENEFITS
54. Chapter 16- 11
• 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.
SUMMARY
55. Chapter 16-
Reading: 16.1 -16.14
Core Problems:
Definition of composite
Longitudinal vs. Transverse Strengths
Rule of Mixtures
Efficiency factor
PMC, CMC, and MMC
0
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