Transcript No Slide Title

Laminated Composite Materials
Mechanical Engineering
Instructor: Autar Kaw
What are you going to learn?
• What are composite materials?
• How are they manufactured?
• What advantages and drawbacks do composites
have over metals?
• Develop mathematical models to understand the
mechanical response of composites to mechanical
and hygrothermal loads?
• Use the above mathematical models to optimally
design structures made of composites.
What is a composite?
• A composite is a structural
material which consists of
combining two or more
constituents
• Examples:
– Flesh in your leg reinforced
with bones
– Concrete reinforced with
steel
– Epoxy reinforced with
graphite fibers.
Bricks and Straw
• “You are no longer to
supply the people with
straw for making
bricks; let them go and
gather their own
straw” - Exodus 5.7.
Shift in Paradigm About Materials
“More important than any one
new application is the new
‘materials’ concept itself ”
Peter F. Drucker
The Age of Discontinuity,
1969
What is this paradigm shift in
materials?
•
•
•
•
From substance to structures
From artisan to science
From workshop to mathematical modeling
From what nature provides to what man can
accomplish
Are Composites Important?
• Considered as one of the ten outstanding
achievements of 1964-1989
From constituents to application
Chapter 1
Introduction to
Composite
Materials
Chapter 1: Objectives
• What is a composite?
• What are the advantages and drawbacks of
composites over monolithic materials?
• What factors influence mechanical properties of a
composite
Chapter Objectives (continued)
•
•
•
•
How do we classify composites?
What are the common types of fibers and matrices?
How are composite materials manufactured?
What are the mechanical properties of composite
materials?
Chapter Objectives (continued)
• Give applications of composite materials.
• How are composites recycled?
• What terminology is used for studying mechanics of
composites?
What is an advanced composite?
• Advanced composites are composite
materials which were traditionally used in
aerospace industries
Examples include graphite/epoxy,
Kevlar/epoxy and Boron/aluminum
Examples of Natural Composites
• Wood
– Cellulose Fibers
– Lignin Matrix
• Bones
– Collagen Fibers
– Mineral Matrix
Fibrous Composites
• Generally there are two phases
– Fiber as a reinforcement
– Matrix as a binder
Historical Perspective
• 4000 B.C. Fibrous composites were used in
Egypt in making laminated writing
materials
• 1300 BC: Reference to Book of Exodus
• 1700 AD: French Scientist, Reumer talked
about potential of glass fibers
Historical Perspectives (continued)
• 1939: Glass fiber manufactured
commercially for high temperature
electrical applications
• 1950s: Boron and carbon fibers were
produced to make ropes.
• 1960s: Matrix added to make polymeric
matrix composites
Historical Perspectives (continued)
• 1970s: Cold war forces development of metal
matrix composites for military aircrafts and
missile guidance systems
• 1990s: High temperature ceramic matrix
composites are being aggressively researched
for use in next generation aircraft engines and
power plant turbines
Shipments of Composites
Total Shipments in 1995: 3.176 x 109 lb [1.441 x 109 kgs]
Appliance Other
& Business
4%
Equipment 5%
Consumer
Products
6%
Electrical
& Electronics
10%
Transportation
31%
CorrosionResistant
Equipment
12%
Marine
12%
Construction
20%
World Market of Composites
Advantages of Composites
•
•
•
•
•
•
Specific Strength and Stiffness
Tailored Design
Fatigue Life
Dimensional Stability
Corrosion Resistance
Cost-Effective Fabrication
Drawbacks of Composites
•
•
•
•
High cost of fabrication of composites
Complex mechanical characterization
Complicated repair of composite structures
High combination of all required properties may
not be available
Composites vs. Metals
Composites vs. Metals
• Comparison based on
six primary material
selection parameters
Why composites over metals?
•
•
•
•
•
High Strength and High Stiffness
Tailored Design
Fatigue Life
Dimensional Stability
Corrosion Resistance
Why Composites over Metals?
• How is the mechanical advantage of
composite measured?
Specific modulus =
Specific strength =
E

,
 ult
.

where
E  Young' s Modulus
  Density
ult
Ultimate Strength
Specific Strength vs. Year
Table 1.1. Specific modulus and strength of typical fibers,
composites and bulk metals
Units
Graphite
Specific Young’s Ultimate
Gravity Modulus Strength
MPa
GPa
2067
230.00
1.8
Unidirectional Graphite/Epoxy
1.6
181.00
1500
0.1131
0.9377
Cross-Ply Graphite/Epoxy
1.8
95.98
373.0
0.06000
0.2331
Quasi-isotropic Graphite/Epoxy 1.8
69.64
276.48
0.04353
0.1728
Steel
7.8
206.8
648.1
0.02652
0.08309
Aluminum
2.6
68.95
275.8
0.02652
0.1061
Material
Specific
Modulus
GPa-m3/kg
0.1278
Specific
Strength
MPa-m3/kg
1.148
Specific Strength
vs
Specific Modulus
5000
3
Specific Strength [Ksi-in /lb]
4500
Graphite Fiber
4000
Unidirectional
Graphite/Epoxy
3500
3000
2500
2000
1500
Cross-Ply
Graphite/Epoxy
Aluminum
1000
500
Quasi-isotropic
Graphite/Epoxy
Steel
0
0
100
200
300
400
Specific Modulus [Msi-in 3 /lb]
500
600
Other Mechanical Parameters
• Are specific modulus and specific
strength the only mechanical
parameters used for measuring the
relative advantage of composites
over metals?
• NO!!
P 
M = 2L   
 E 
2
cr
1/ 2
P 
 2L  

2
cr
1/ 2

E
Tailored Design
• Engineered to meet specific demands as
choices of making the material are many
more as compared to metals.
• Examples of choices
–
–
–
–
fiber volume fraction
layer orientation
type of layer
layer stacking sequence
Fatigue Life
• Fatigue life is higher than metals such as
aluminum.
• Important consideration in applications such
as
– aircrafts
– bridges
– structures exposed to wind
Dimensional Stability
• Temperature changes can result
– in overheating of components (example
engines)
– thermal fatigue due to cyclic temperature
changes (space structures)
– render structures inoperable (space antennas)
Corrosion Resistance
• Polymers and ceramics matrix are corrosion
resistant
• Examples include
–
–
–
–
underground storage tanks
doors
window frames
structural members of offshore drilling
platforms
What is most limiting factor in the use
of composites in structures?
Lack of engineers with the
knowledge and experience to
design with these materials!!!!
Cost Considerations
• Composites may be more expensive per pound
than conventional materials. Then why do we
use composite materials?
Factors in Cost Estimate
• For Composite Materials
– Fewer pounds are required
– Fabrication cost may be lower
– Transportation costs are generally lower
– Less maintenance than conventional
materials is required
Fiber Factors
• What fiber factors contribute to the
mechanical performance of a
composite?
• Length
• Orientation
• Shape
• Material
Fiber Factor - Length
• Long Fibers
–
–
–
–
Easy to orient
Easy to process
Higher impact resistance
Dimensional stability
• Short Fibers
– Low Cost
– Fast cycle time
Fiber Factor - Orientation
• One direction orientation
– High stiffness and strength in that direction
– Low stiffness and strength in other directions
• Multi-direction orientation
– Less stiffness but more direction independent
Fiber Factor - Shape
• Most common shape is circular
• Hexagon and square shapes give high
packing factors
Fiber Factor - Material
• Graphite and aramids have high strength
and stiffness
• Glass has low stiffness but cost less
Matrix Factors
• What are the matrix factors which
contribute to the mechanical
performance of composites?
– Binds fibers together
– Protects fibers from environment
– Shielding from damage due to handling
– Distributing the load to fibers.
Factors Other Than
Fiber and Matrix
• Fiber-matrix interface
– Chemical bonding
– Mechanical bonding
Fiber Types
•
•
•
•
Glass Fiber (first synthetic fiber)
Boron (first advanced fiber)
Carbon
Silicon Carbide
Types of Matrices
• Polymers
• Metals
• Ceramics
Polymer Matrix
• Thermosets
– polyester
– epoxy
– polymide
• Thermoplastics
– polypropylene
– polyvinyl chloride
– nylon
Metal Matrix
• Aluminum
• Titanium
• Copper
Ceramic Matrix
•
•
•
•
Carbon
Silicon Carbide
Calcium AluminoSilicate
Lithium AluminoSilicate
Why do fibers have thin diameter?
• Less flaws
• More toughness and ductility
• Higher flexibility
Thin Fiber
Thick Fiber
Fiber Strengh [GPa]
Less Flaws
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
5.0
7.0
9.0
11.0
Fiber Diameter [m]
13.0
More Toughness and Ductility
• Fiber-matrix interface area is inversely
proportional to the diameter of the fibers
• Higher surface area of fiber-matrix interface
results in higher ductility and toughness,
and better transfer of loads.
More Flexibility
• Flexibility is proportional to inverse of
• Young’s modulus
• Fourth power of diameter
• Thinner fibers hence have a higher
flexibility and are easy to handle in
manufacturing.
Classification
Particulate Composites
• CONCRETE:
Gravel, sand and
cement
• PAINT: Paint and
aluminum flakes
Flake Composites
• GRAPHITE/EPOXY
Graphite fibers in
epoxy matrix
Fiber Composites
Polymer Matrix Composites
• What are the most common advanced
composites?
– Graphite/Epoxy
– Kevlar/Epoxy
– Boron/Epoxy
Polymer Matrix Composites
• What are the drawbacks of polymer matrix
composites?
– Low operating temperatures
– High CTE and CMEs
– Low elastic properties in certian directions
Are Carbon and Graphite the
Same?
• No
– Carbon fibers have 93%-95% carbon
content and graphite has >99%
carbon content
– Carbon fibers are produced at 2400o
F and graphite fibers are produced at
3400o F
Table 1.4. Typical mechanical
properties of polymer matrix composites
and monolithic materials
Property
Units
Specific Gravity
Graphite Glass/ Steel
/Epoxy Epoxy
1.6
1.8
7.8
Aluminum
2.6
Young’s modulus
Msi
26.25
5.598
30.0
10.0
Ultimate Tensile Strength
Ksi
217.6
154.0
94.0
40.0
0.01111
4.778
6.5
12.8
Coefficient of Thermal Expansion in/in/F
Comparative Stiffness of PMCs
and Metals
How to make a PMC
Schematic of Prepreg
Manufacturing
Controlled Heating Elements
Back-up Material
(Release Film)
Metering Device
Fiber Collimator
Take-up
Roll
Fiber Package
Resin Solution
Prepreg Boron/Epoxy
Autoclave Lamination
Filament Winding
Tension Adjust
Resin Coated Fibers
Resin Bath
Rotating Mandrel
Fiber
Roving
(b) Mat
(a) Preform
Clamp
Resin
Transfer
Molding
Mould Closure
Heat
Resin Injection and Air
Displacement
Heat
Resin
Cure
De-Moulding
Mould Fill and Resin Overspill
Trimming
Common PMC Fibers &
Matrices
• Fibers
– Graphite
– Glass
– Kevlar
• Matrices
– Epoxy
– Phenolic
– Polyester
Table 1.5 Typical mechanical
properties of fibers used in polymer
matrix composites
Property
Specific Gravity
Units
Graphite
18.
Aramid
1.4
Glass
2.5
Steel
7.8
Aluminum
2.6
Young’s modulus
Msi
33.35
17.98
12.33
30
10
Ultimate Tensile Strength
Ksi
299.8
200.0
224.8
94
40
Axial Coefficient of Thermal Expansion
in/in/F
-0.722
-2.778
2.778
6.5
12.8
Cost Comparison of PMC fibers
Type of fiber
A-glass
C-glass
E-glass
S-2 Glass
Heavy Tow
Medium Tow
Low Tow
Kev29
Kev149
Cost ($ per pound)
.65 - .90
.75 - 1.00
.75 - 1.00
6.00 - 8.00
9.00 - 12.00
15.00 -20.00
40.00 -70.00+
12.00 -14.00
25.00 -30.00
Manufacturing of Glass Fibers
Glass Feedstock
Electrically Heated Furnace
Protective Sizing Operation:
Water or Solvent Based
Glass Filaments
Filaments Collected Together to
Form a Strand
Glass Strand Wound
onto a Forming Tube
and Oven Dried to
Remove Water/Solvent
Chopping
Operation
Untwisted
Strand
Roving
Twisting of Strand
Weaving
Woven Fabric
Woven
Roving
Chopped Strand
Application of Resin
Binder
Chopped Strand
Mat
Glass Fiber Types
•
•
•
•
•
•
E-glass (fiberglass) - electrical applications
S-glass - strength applications
C-glass - Corrosion resistant
D-glass - Low dielectric applications
A-glass - Appearance applications
AR-glass - Alkali resistant
Table 1.6 Comparison of
properties of E-glass and S-glass
Property
Specific Gravity
Units
E-glass
2.54
S-glass
2.49
Young’s modulus
Msi
10.5
12.4
Ultimate Tensile Strength
Ksi
500
665
Coefficient of Thermal Expansion
in/in/F
2.8
3.1
Table 1.7 Chemical Composition
of E-Glass and S-glass Fibers
% Weight
S-glass
64
Material
Silicon Oxide
E-glass
54
Aluminum Oxide
15
25
Calcium Oxide
17
0.01
Magnesium Oxide
4.5
10
Boron Oxide
8
0.01
Others
1.5
.8
Fig 1.11 Manufacturing
Graphite Fibers
Stretching
Stabilization (200-300oC)
Off-Wind Creel
Carbonization (1000-1500oC)
Graphitization (2500oC)
Wind-Up Creel
Surface Treatment
Resin Systems
•
•
•
•
•
Polyester
Phenolics
Epoxy
Silicone
Polymide
Properties of epoxy
PROPERTY
UNITS EPOXY
Specific gravity
-
1.28
Young’s modulus Msi
0.55
UTS
12.0
Ksi
Curing Stages of Epoxy
Comparison of Resins
Difference between thermosets
and thermoplastics
THERMOPLASTICS
THERMOSET
Soften on heating and pressure, and hence
easy to repair
High strains to failure
Decompose on heating
Indefinite shelf life
Definite shelf life
Can be reprocessed
Cannot be reprocessed
Not tacky and easy to handle
Tacky
Short cure cycles
Long cure cycles
Low strains to failure
Higher fabrication temperature and
Lower fabrication
viscosities have made it difficult to process temperature
Excellent solvent resistance
Fair solvent resistance
Pre-Preg Graphite/Epoxy
Application of Polymer Matrix
Composites
Carbon-fiber shin
Space Shuttle
Jet Skis
Lear Fan
Fighter Jets
Corvette Leaf Springs
Snow Skis
I-beam
Pressure vessels
Metal Matrix Composites
• What are metal-matrix composites?
Metal matrix composites have a metal
matrix.
Examples include silicon carbide fibers in
aluminum, graphite fibers in aluminum.
Advantages of MMCs
• Higher specific strength and modulus over
metals.
• Lower coefficients of thermal expansion
than metals by reinforcing with graphite.
• Maintenance of high strength properties at
high temperatures.
Degrading properties in MMCs
(Fig 1.3)

2a

• Are there any properties
which degrade when
metals are reinforced with
fibers?
Yes, they may have
reduced ductility and
fracture toughness.
Typical mechanical properties of metal matrix composites
Property
Units
Specific Gravity
SiC/
Aluminum
2.6
Graphite/
Aluminum
2.2
Steel
Aluminum
7.8
2.6
Young’s modulus
Msi
17
18
30
10
Ultimate Tensile Strength
Ksi
175
65
94
34
6.9
10
6.5
12.8
Coefficient of Thermal Expansion in/in/F
Boron Fiber
Step 0: Cutting the shape
Step 1: Apply Aluminum File
Step 3: Lay Up Desired Plies
Step 4:Vacuum the specimen
TEP 4:
TO VACUUM
VACUUME
VACUUM
ENCAPSULATE
Step5: Heat to Fabrication
Temperature
: HEAT TO FABRICATION TEMPERATURE
HEAT
HEAT
Step 6: Apply Pressure and Hold
for Consolidation Cycle
PPLY PRESSURE AND HOLD FOR CONSOLIDATION CYCLE
OL, REMOVE AND CLEAN PART
Step 7: Cool, Remove and Clean
Part
Foil
Fiber Mat
Foil
(a)
Stack
Consolidate
(c)
Schematic of
Diffusion
Bonding
(b)
(d)
Heat and Pressure
Clean and
Trim + NDE
(e)
Secondary Fabrication
(f)
Silicon Carbide/ Aluminum
Composite
Application of MMCs
Application of MMCs
Application of MMCs
Ceramic Matrix Composites
• What are ceramic matrix composites?
• Ceramic matrix composites have
matrices of alumina, calcium alumino
silicate (CAS), lithium alumino silicate
(LAS). Examples include Silicon
Carbide/CAS and Carbon/LAS.
Advantages of CMCs
• High strength, hardness and high
service temperatures
• Chemical inertness
• Low Density
Table 1.12 Typical fracture toughness
of monolithic materials and ceramic
matrix composites
Material
Epoxy
Fracture Toughness, MPa m
3
Fracture Toughness, Ksi in
2.73
Aluminum Alloys 35
31.85
Silicon Carbide
3
2.73
SiC/Al2O3
27
24.6
SiC/SiC
30
27.3
Table 1.13 Typical mechanical
properties of some ceramic matrix
composites
Property
Specific Gravity
Units
SiC/LAS
2.1
SiC/CAS
2.5
Steel Aluminum
7.8
2.6
Young’s modulus
Msi
13
17.55
30.0
10.0
Ultimate Tensile Strength
Ksi
72
58.0
94.0
34.0
2.5
6.5
12.8
Coefficient of Thermal Expansion in/in/F 2
Glass Impregnated
Fiber Tape
Fibers
Glass Slurry Tank
Binder Burnout
500oC
Stack of Glass Impregnated
Fiber Tapes
Pressure
Hot Pressing
800 - 925oC
Fiber/Glass Composite
Manufacturing of
Ceramic Matrix
Composites Slurry
Infiltration
Application of CMCs
Carbon-Carbon Compoistes
• What are carbon-carbon
composites?
Carbon - Carbon composites
have carbon fibers in carbon
matrix.
Advantages of Carbon-Carbon
Composites
•
•
•
•
•
•
Gradual failure
Withstand high temperatures
Low creep at high temperatures
Low density
High thermal conductivity
Low and tailorable Coefficient of Thermal
Expansion
Advantages of Carbon-Carbon
Composites
• Great strength to weight ratio
• High modulus, thermal conductivity, and
electrical conductivity
• Good thermal shock resistance, abrasion
resistance, and fracture toughness
• Excellent high temperature durability in
inert or vacuum environment
• Good corrosion resistance
Table 1.14 Typical mechanical
properties of carbon-carbon matrix
composites
Property
Specific Gravity
Units
C-C
1.68
Steel Aluminum
7.8
2.6
Young’s modulus
Msi
1.95
30
10
Ultimate Tensile Strength
Ksi
5.180
94
34
6.5
12.8
Coefficient of Thermal Expansion in/in/F 1.11
Carbon-Carbon Manufacturing
(Fig 1.34)
Step 1
Standard
Gr/Phenolic
Prepreg
Lay-up
and
Cure
Step 2
Pyrolysis
Step 4
Step 5
Coating
Sealing
After 3 Impregnations
Resin
Impregnation
Step 3
Applications of C-C Composites
• Space Shuttle Nose Cones
– Re-entry temperature of 3092 K
• Aircraft Brakes
– Saves 450 kgs of mass
– Two-four times durability vs. steel
– 2.5 times specific heat of steel
Recycling of Composites
• What types of process are used for
recycling of composites?
• Why is recycling of composites
complex?
• What can one do if one cannot separate
different types of composites?
Recycling Continued
• What are the various steps in
mechanical recycling of short fiberreinforced composites?
• Where are mechanically recycled short
fiber composites used?
Chemical Recycling
Which chemical process shows the
most promise?
•Why is chemical recycling not as
popular as mechanical recycling?
•
Definitions
•
•
•
•
•
•
Isotropic body
Homogeneous body
Anisotropic body
Nonhomogeneous body
Lamina
Laminate
+
Fiber
Matrix
Micromechanics of
a Lamina (Chapter 3)
Macromechanics of a Lamina
(Chapter 2)
Homogeneous Orthotropic
Layer
Macromechanics of a Laminate
(Chapter 4)
Analysis and Design of Laminated
Structures (Chapter 5)
Structural Element
Laminate
Schematic
of Analysis
of
Laminated
Composites
An Artist’s Rendition of a
Composite Material