View
841
Download
5
Category
Tags:
Preview:
Citation preview
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?
2
Pole-vaulting
Lightweight - low densityBuckling resistance - stiffnessStrong - yield strengthMinimal twistingCost
3
Boeing 757-200
4
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
5
Terminology/Classification• Composites: -- Multiphase material w/significant proportions of each phase.
• 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
• Matrix: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment -- Classification: MMC, CMC, PMC
metal ceramic polymer
Reprinted with permission fromD. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47.
woven fibers
cross section view
0.5mm
0.5mm
6
Factors influence Composite properties
Properties of the reinforcement material
Matrix–reinforcement
bonding/adhesion
Properties of the matrix material
Mode of fabrication
Ratio of matrix to
reinforcement
7
Functions of the continuous matrix phase: Bind fibers together, applied stress distributed
among the fibers Protect the fibers from being damaged Separate the fibers, inhibit crack propagation
Characteristics of fiber and matrix: Matrix phase – ductile, soft, low elastic modulus Fiber phase – stiff, strong, brittle
Strong interfacial bond between fiber-matrix: maximize stress transmittance minimize fiber pull-out and failure
8
Composite Survey
L arg e-p artic le
D isp ers ion -s tren g th en ed
P artic le -re in fo rced
C on tin u ou s(a lig n ed )
A lig n ed R an d om lyorien ted
D iscon tin u ou s(sh ort)
F ib er-re in fo rced
L am in a tes S an d w ichp an e ls
S tru c tu ra l
C om p os ites
Adapted from Fig. 16.2, Callister 7e.
9
Composite Survey: Particle-I
• Examples:Adapted from Fig. 10.19, Callister 7e. (Fig. 10.19 is copyright United States Steel Corporation, 1971.)
- Spheroidite steel
matrix: ferrite (a)(ductile)
particles: cementite (Fe3C)
(brittle)60 mm
Adapted from Fig. 16.4, Callister 7e. (Fig. 16.4 is courtesy Carboloy Systems, Department, General Electric Company.)
- WC/Co cemented carbide
matrix: cobalt (ductile)
particles: WC (brittle, hard)Vm:
10-15 vol%! 600 mmAdapted from Fig. 16.5, Callister 7e. (Fig. 16.5 is courtesy Goodyear Tire and Rubber Company.)
- Automobile tires
matrix: rubber (compliant)
particles: C (stiffer)
0.75 mm
Particle-reinforced Fiber-reinforced Structural
10
Composite Survey: Particle-II
Concrete – gravel + sand + cement - Why sand and gravel? Sand packs into gravel voids
Particle-reinforced Fiber-reinforced Structural
• Concrete consists of an aggregate of particles that are bonded together by a cement.
• Limitations of concrete: weak and brittle material large thermal expansions - changes in temperature may crack when exposed to freeze-thaw cycles
• Three reinforcement strengthening techniques:1. reinforcement with steel wires, rods, etc2. reinforcement with fine fibers of a high modulus material3. introduction of residual compressive stresses by prestressing or
posttensioning.
12
Composite Survey: Particle-III
• Elastic modulus, Ec, of composites: -- two approaches.
For equal volume of fibers:• Upper limit: isostrain conditions, higher modulus• Lower limit: isostress conditions, lower modulus
Adapted from Fig. 16.3, Callister 7e. (Fig. 16.3 is from R.H. Krock, ASTM Proc, Vol. 63, 1963.)
lower limit:1
Ec= Vm
Em+
Vp
Ep
c m m
upper limit:E = V E + VpEp
“rule of mixtures”
Particle-reinforced Fiber-reinforced Structural
Data: Cu matrix w/tungsten particles
0 20 40 60 80 100
150
200
250
300
350
vol% tungsten
E(GPa)
(Cu) (W)
13
Composite Survey: Fiber-I
• 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
Particle-reinforced Fiber-reinforced Structural
14
Why fiberglass-reinforced composites are utilized extensively?
inexpensive to producecomposites have relatively high specific
strengthschemically inert in a wide variety of
environmentsLimitations of these composites?care in handling the fibers, susceptible to
surface damagelacking in stiffness in comparison to other
fibrous compositeslimited maximum temperature use
15
• 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
• 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.
16
Glass fibers
• low tensile modulus• relatively high specific gravity (among the
commercial fibers) • sensitivity to abrasion with handling (which
frequently decreases tensile strength)• relatively low fatigue resistance• high hardness (which causes excessive wear on
molding dies and cutting tools)
• Disadvantages:
17
Glass fibers
E-glass High-strength glass
S-glass
S-2 glass
S-2 hollow glass fiber
C-glass
Categories
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 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.
Glass fibers
19
Composite Survey: Fiber-II
• Fiber Materials– Whiskers - Thin single crystals - large length to diameter ratio
• graphite, SiN, SiC• high crystal perfection – extremely strong, strongest known• very expensive
Particle-reinforced Fiber-reinforced Structural
– Fibers• polycrystalline or amorphous• generally polymers or ceramics• Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE
– Wires• Metal – steel, Mo, W
20
Fiber Alignment
alignedcontinuous
aligned randomdiscontinuous
Adapted from Fig. 16.8, Callister 7e.
21
Composite Survey: Fiber-III
• Aligned Continuous fibers• 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.
Particle-reinforced Fiber-reinforced Structural
matrix: a (Mo) (ductile)
fibers: g’ (Ni3Al) (brittle)
2 mm
-- Ceramic: Glass w/SiC fibers formed by glass slurry
Eglass = 76 GPa; ESiC = 400 GPa.
(a)
(b)
fracture surface
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 CRCPress, Boca Raton, FL.
22
Composite Survey: Fiber-IV
• 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.
• 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, 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.
Particle-reinforced Fiber-reinforced Structural
(b)
fibers lie in plane
view onto plane
C fibers: very stiff very strong
C matrix: less stiff less strong
(a)
23
Composite Survey: Fiber-V
• Critical fiber length for effective stiffening & strengthening:
• Ex: For fiberglass, fiber length > 15 mm needed
Particle-reinforced Fiber-reinforced Structural
c
f d
15length fiber
fiber diameter
shear strength offiber-matrix interface
fiber strength in tension
• Why? Longer fibers carry stress more efficiently!Shorter, thicker fiber:
c
f d
15length fiberLonger, thinner fiber:
Poorer fiber efficiency
Adapted from Fig. 16.7, Callister 7e.
c
f d
15length fiber
Better fiber efficiency
s(x) s(x)
24
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
mm
ff
m
f
VE
VE
F
F f = fiber
m = matrix
25
Composite Strength: Transverse Loading
In transverse loading the fibers carry less of the load - isostress
c = m = f = c= mVm + fVf
f
f
m
m
ct E
V
E
V
E
1transverse modulus
26
Composite Strength
• Estimate of Ec and TS for discontinuous fibers:
-- valid when
-- Elastic modulus in fiber direction:
-- TS in fiber direction:
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)
(aligned 1D)
Values from Table 16.3, Callister 7e. (Source for Table 16.3 is H. Krenchel, Fibre Reinforcement, Copenhagen: Akademisk Forlag, 1964.)
c
f d
15length fiber
Particle-reinforced Fiber-reinforced Structural
(TS)c = (TS)mVm + (TS)fVf
Ec = EmVm + KEfVf
27
Yarns
Chopped strands
Woven fabric
Fiber forms
28
Matsbidirectional unidirectional
X-mat
Roving
Fiber forms
29
Composite Production Methods-I
Pultrusion Continuous fibers pulled through resin tank,
then preforming die & oven to cure
Adapted from Fig. 16.13, Callister 7e.
Performs of desired shape,Establishes the resin/fiber ratio
Precision machine toimpart the final shape
30
Pultrusion
The advantages are:Process may be automatedHigh production ratesVariety of shapes,constant cross-sections,
long pieces may be producedThe disadvantage – shapes are limited to
those having a constant cross-section.
31
Composite Production Methods-II
Filament Winding Ex: pressure tanks Continuous filaments wound onto mandrel to form a hollow (usually cylindrical) shape
Adapted from Fig. 16.15, Callister 7e. [Fig. 16.15 is from N. L. Hancox, (Editor), Fibre Composite Hybrid Materials, The Macmillan Company, New York, 1981.]
32
Filament Winding
The advantages are: Process may be automatedVariety of winding patterns are possibleHigh degree of control over winding
uniformity and orientation The disadvantage – variety of shapes is
limited
33
Composite Survey: Structural
• Stacked and bonded fiber-reinforced sheets -- stacking sequence: e.g., 0º/90º -- benefit: balanced, in-plane stiffness
Adapted from Fig. 16.16, Callister 7e.
Particle-reinforced Fiber-reinforced Structural
• Sandwich panels -- low density, honeycomb core -- benefit: small weight, large bending stiffness
honeycombadhesive layer
face sheet
Adapted from Fig. 16.18,Callister 7e. (Fig. 16.18 isfrom Engineered MaterialsHandbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)
34
Composite Benefits
• CMCs: Increased toughness
fiber-reinf
un-reinf
particle-reinfForce
Bend displacement
• PMCs: Increased E/r
E(GPa)
G=3E/8K=E
Density, r [mg/m3].1 .3 1 3 10 30
.01
.1
1
10102
103
metal/ metal alloys
polymers
PMCs
ceramics
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.
• MMCs: Increased creep resistance
20 30 50 100 20010-10
10-8
10-6
10-4
6061 Al
6061 Al w/SiC whiskers s(MPa)
ess (s-1)
35
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.
Recommended