Composite Materials 1
ISSUES TO ADDRESS...
• What are the classes and types of composites?
• Why are composites composites used instead of metals, ceramics, or polymers? • How do we estimate composite stiffness & strength? strength? • What are some typical applications?
Pole-vaulting 2
Lightweight - low density Buckling resistance - stiffness Strong - yield strength Minimal twisting Cost
3
Boeing 757-200
Composites 4
Combine
materials with the objective of getting a more desirable combination of properties Ex: get flexibility & weight of a polymer plus plus the strength of a ceramic
Principle
of combined action Mixture gives “averaged” properties
Terminology/Classification • Composites Composites::
5 -- Multiphase material w/significant proportions of each phase.
woven fibers
• Matrix Matrix:: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment
-- Classification: metal
MMC, CMC, PMC
ceramic
0.5mm cross section view
polymer
• Dispersed phase: phase: -- Purpose: enhance matrix properties. MMC:: increase σ y , TS , creep resist. MMC CMC: increase Kc CMC: PMC:: increase E , σ y , TS , creep resist. PMC
-- Classification: Particle Particle,, fiber , structural
0.5mm Reprinted with permission from D. Hull and T.W. Clyne, An Clyne, An Introduction to Composite Materials, Materials , 2nd ed., Cambridge University Press, New York, York, 1996, Fig. 3.6, p. 47.
Properties of the matrix material
6
Properties of the reinforcement material
Factors influence Composite properties Ratio of matrix to reinforcement
Matrix– reinforcement bonding/adhesion Mode of fabrication
7
Functions
of the continuous matrix phase: ü Bind fibers together, applied stress distributed among the fibers ü Protect the fibers from being damaged ü Separate the fibers, inhibit crack propagation
Characteristics
of fiber and matrix: Ø Matrix phase – ductile, soft, low elastic e lastic modulus Ø Fiber phase – stiff, strong, brittle
Strong
interfacial bond between fiber-matrix: ü maximize stress transmittance ü minimize fiber pull-out and failure
Composite Survey 8 C
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L a r g e p a r t i c
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D s
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F
p n
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S
i s c o n ( s h o r
n
R o
a n r i e
L
a
m
t r u
i n
c
S
t u
a p
d n
Adapted from Fig. 16.2, Callister 7e. 7e.
n a
d n
e
Composite Survey: Particle-I Particle-reinforced • Examples: - Spheroidite matrix: ferrite (α ) steel
9
Fiber-reinforced
(ductile)
60 µ m
- WC/Co cemented carbide
matrix: cobalt (ductile) V m : 10-15 vol%!
Structural particles: cementite (Fe3 C) (brittle)
particles: WC (brittle, hard)
Adapted from Fig. 10.19, Callister 7e. 7e. (Fig. 10.19 is copyright United States Steel Corporation, 1971.)
Adapted from Fig. 16.4, Callister 7e. 7e. (Fig. 16.4 is courtesy Carboloy Systems, Department, General Electric Company.)
600 µ m
- Automobile matrix: rubber tires
particles: C (stiffer)
(compliant) 0.75 µ m
Adapted from Fig. 16.5, Callister 7e. 7e. (Fig. 16.5 is courtesy Goodyear Tire and Rubber Company.)
Composite Survey: Particle-II Particle-reinforced
10
Fiber-reinforced
Structural
Concrete – gravel + sand + cement - Why sand and gravel? gravel?
Sand packs into gravel voids
Concrete consists of an aggregate of particles that are bonded together by a cement. Limitations of concrete: üweak and brittle material ülarge thermal expansions - changes in temperature ümay crack when exposed to freeze-thaw f reeze-thaw cycles
•
•
Three reinforcement strengthening techniques: 1.reinforcement with steel wires, rods, etc 2.reinforcement with fine fibers of a high modulus material 3.introduction of residual compressive stresses by posttensioning.
•
prestressing
or
Composite Survey: Particle-II Particle-reinforced
11
Fiber-reinforced
Structural
Concrete – gravel + sand + cement - Why sand and gravel? gravel?
Sand packs into gravel voids
Reinforced concrete - Reinforce with steel, rod or mesh - 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
Post tensioning – tighten nuts to put under tension
nut
threaded rod
Composite Survey: Particle-III Particle-reinforced
12
Fiber-reinforced
Structural
• Elastic modulus, modulus, E c c, of composites: -- two approaches.
upp pper er lim imit it:: “rule of mixtures” E c = VmE m + V pE p
E (GPa) (GPa) 350
Data: 30 0 Cu matrix 300 w/tungsten 250 particles 200 20 0 150 0
(Cu)
lower limit: V 1 V = m + p E c E m E p 20 4 0
60 80
Adapted from Fig. 16.3, is Callister 7e. 7e. (Fig. 16.3 is from R.H. Krock, ASTM Krock, ASTM Proc , Vol. 63, 1963.)
10 0 vol% tungsten
(W)
For equal volume of fibers: • Upper limit: isostrain conditions, higher modulus Lower limit: isostress conditions, lower modulus m odulus
•
Composite Survey: Fiber-I Particle-reinforced
13
Fiber-reinforced
Structural
Fibers very strong Provide significant 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
• • •
Why
fiberglass-reinforced composites are utilized extensively? 14 üinexpensive to produce ücomposites have relatively high specific strengths üchemically inert in a wide variety of environments Limitations of these composites? care in handling the fibers, susceptible to surface damage lacking in stiffness in comparison to other fibrous composites limited maximum temperature use
Glass fibers 15
Glass fibers are amorphous (noncrystalline) and isotropic (equal properties in all directions) and are a long, three-dimensional network of silicon, oxygen, and other atoms arranged in a random fashion.
•
Characteristics:
•
an inorganic, synthetic, multifilament material are the most common of all reinforcing fibers for polymeric (plastic) matrix composites strong, low in cost, nonflammable, nonconductive (electrically), and corrosion resistant.
•
•
•
Glass fibers 16
Disadvantages:
•
low tensile modulus relatively relatively high specific gravity (among (am ong the commercial fibers) sensitivity to abrasion with handling (which frequently decreases tensile strength) relatively relatively low fatigue resistance high hardness (which causes excessive wear on molding dies and cutting tools) • •
•
• •
Glass fibers 17
Categories
E-glass
High-strength glass
S-glass
C-glass
S-2 hollow glass fiber S-2 glass
Glass fibers 18
Applications:
•
E-glass has the lowest cost of all commercially available reinforcing fibers, which is the reason for its widespread use in the fiber-reinforced plastics (FRP) industry.
–
S-glass, originally developed for aircraft S-glass, components and missile casings, has the highest tensile strength among all fibers in use. However, the compositional difference and higher manufacturing cost make it more expensive than E-glass.
–
Composite Survey: Fiber-II Particle-reinforced
19
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
Fiber Alignment 20 Adapted from Fig. 16.8, Callister 7e. 7e.
aligned continuous
aligned random discontinuous
Compositee Survey: Fiber-III Composit 21
Particle-reinforced Fiber-reinforced • Aligned Continuous fibers • Examples: -- Metal Metal::
γ
'(Ni3Al)-α (Mo)
by eutectic solidification.
matrix:
α
(Mo) (ductile)
-- Ceramic Ceramic:: Glass w/SiC fibers formed by glass slurry E glass glass = 76 GPa; E SiC SiC = 400 GPa.
(a)
2µ m
fibers: γ ’ (Ni3Al) (brittle) From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. AVol. AVol. 19(4), pp. 987-998, 1988. Used with permission. permission.
Structural
(b)
fracture surface From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Science, Reprint ed., CRC Press, Boca Raton, FL, 2000. (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig. 11.20, 11.20, p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Rawlings). Used with permission of CRC Press, Boca Raton, FL.
Composite Survey: Fiber-IV 22
Particle-reinforced Fiber-reinforced • 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)
(a)
Structural C fibers: very stiff very strong
C matrix: less stiff view onto plane less strong fibers lie in plane
• Other variations: -- Discontinuous, random 3D -- Discontinuous, 1D
Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, 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.
Composite Survey: Fiber-V 23
Particle-reinforced Fiber-reinforced Structural • Critical fiber length for effective stiffening & strengthening: fiber strength in tension
fiber length > 15
fiber diameter σ f d τc
shear strength of fiber-matrix interface
• Ex: For fiberglass, fiber length > 15 mm needed more efficiently! efficiently! • Why? Longer fibers carry stress more Shorter,, thicker fiber: Shorter
fiber length < 15 σ (x)
σ f d
Longer, thinner fiber:
fiber length > 15
σ f d τ c
τ c σ (x)
Adapted from Fig. 16.7, Callister 7e. 7e.
Poorer fiber efficiency
Better fiber efficiency
Composite Strength: Longitudinal Loading 24
Continuous fibers - Estimate fiber-reinforced composite strength
for long continuous fibers in a matrix
Longitudinal deformation
c
=
mV m +
f V f
but
c=
m=
f
∴
volume fraction
E ce = E m V m + E f V f F f F m
=
E f V f E mV m
isostrain
longitudinal (extensional) modulus f = fiber m = matrix
Compositee Strength Composit Strength:: Transverse Loading 25
In
transverse loading the fibers carry less of the load isostress c= m = f = c= mV m + f V f
1 E ct
=
V m E m
+
V f E f
transverse modulus
Composite Strength Particle-reinforced
26
Fiber-reinforced
Structural
• Estimate of E of E c TS for discontinuous fibers: c and TS for -- valid when fiber length
>
15
σ f d τ c
-- Elastic modulus in fiber direction:
E c = E mV m + K E Ef V f efficiency factor : -- aligned 1D: K = 1 (aligned ) -- aligned 1D: K = 0 (aligned ) -- random 2D: K = K = 3/8 (2D isotropy) -- random 3D: K = K = 1/5 (3D isotropy)
Values from Table 16.3, Callister 7e. 7e. (Source for Table Table 16.3 is H. Krenchel, Fibre Reinforcement , Copenhagen: Akademisk Forlag, 1964.)
-- TS in in fiber direction:
(TS )c = (TS )mV m + (TS )f V f
(aligned 1D)
Fiber forms 27
Chopped strands
Yarns
Woven fabric fabr ic
Fiber forms 28
X-mat bidirectional unidirectional
Roving
Mats
Composite Production Methods-I Pultrusion
29
Continuous fibers pulled through resin tank, then preforming die & oven to cure Precision machine to impart the final shape
Performs of desired shape, Establishes the resin/fiber ratio
Adapted from Fig. 16.13, Callister 7e. 7e.
Pultrusion 30
The
advantages are: üProcess may be automated üHigh production rates ü Variety of shapes,constant cross-sections, long pieces may be produced The disadvantage – shapes are limited to those having a constant cross-section.
Composite Production Methods-II Filament
Winding
31
Ex: pressure tanks Continuous filaments wound onto mandrel to form a hollow (usually cylindrical) shape
Adapted from Fig. 16.15, Callister 7e. 7e. [Fig. 16.15 is from N. L. Hancox, (Editor), Fibre Composite Hybrid Materials, The Macmillan Company, New York, 1981.]
Filament Winding 32
The
advantages are: üProcess may be automated ü Variety of winding patterns are possible üHigh degree of control over winding uniformity and orientation The disadvantage – variety of shapes is limited
Composite Survey: Structural Particle-reinforced
33
Fiber-reinforced
Structural
• Stacked and bonded fiber-reinforced sheets º
-- stacking sequence: e.g., 0º/90 -- benefit: balanced, in-plane stiffness Adapted from Fig. 16.16, Callister 7e. 7e.
• Sandwich panels -- low density, honeycomb core -- benefit: benefit: small weight, large bending stiffness face sheet adhesive layer honeycomb Adapted from Fig. 16.18, Callister 7e. 7e. (Fig. 16.18 is from Engineered Materials Handbook , Vol. 1, Composites, Composites, ASM International, Materials Park, OH, 1987.)
Composite Benefits • CMCs: Increased toughness34 Force
E (GPa) (GPa) PMCs 2 10 10
fiber-reinf
1
un-reinf
10
-4
-1 ss (s ) -6 10
Increased creep resistance
10 10
-8
-10
metal/ metal alloys
.1 G=3E =3E /8 /8 polymers .01 K =E .1 .3 1 3 10 30 Density, ρ [mg/m3]
Bend displacement
• MMCs:
ceramics
103
particle-reinf
ε
• PMCs: Increased E /ρ
6061 Al
6061 Al w/SiC whiskers
20 30 3 0 50
Adapted from T.G. T.G. Nieh, "Creep rupture of a silicon-carbide reinforced aluminum composite", Metall. Trans. AVol. AVol. 15(1), pp. 139-146, 1984. Used with with permission. permission.
σ (MPa)
100 200
Summary 35 • Composites are classified according to:
-- the matrix material (CMC (CMC,, MMC MMC,, PMC PMC)) -- the reinforcement geometry (particles, fibers, layers).
• Composites enhance matrix properties: -- MMC: enhance σ y , TS , creep performance -- CMC: enhance K c c -- PMC: enhance E , σ y , TS , creep performance • Particulate-reinforced: -- Elastic modulus can be estimated. -- Properties are isotropic. • Fiber-reinforced: -- Elastic modulus and TS can TS can be estimated along fiber dir. dir. -- Properties can be isotropic or anisotropic. • Structural: -- Based on build-up of sandwiches in layered form.
