Laminated%20Composite%20Materials%20Mechanical%20Engineering%20Instructor:%20Autar%20Kaw

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Laminated Composite MaterialsMechanical
EngineeringInstructor Autar Kaw
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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.

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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.

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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.

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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

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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

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Are Composites Important?

• Considered as one of the ten outstanding
  achievements of 1964-1989

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From constituents to application
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Chapter 1Introduction to Composite Materials
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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

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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?

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Chapter Objectives (continued)

• Give applications of composite materials.
• How are composites recycled?
• What terminology is used for studying mechanics
  of composites?

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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

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Examples of Natural Composites

• Wood
• Cellulose Fibers
• Lignin Matrix
• Bones
• Collagen Fibers
• Mineral Matrix

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Fibrous Composites

• Generally there are two phases
• Fiber as a reinforcement
• Matrix as a binder

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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

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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

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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

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Shipments of Composites
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World Market of Composites
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Advantages of Composites

• Specific Strength and Stiffness
• Tailored Design
• Fatigue Life
• Dimensional Stability
• Corrosion Resistance
• Cost-Effective Fabrication

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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

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Composites vs. Metals
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Composites vs. Metals

• Comparison based on six primary material
  selection parameters

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Why composites over metals?

• High Strength and High Stiffness
• Tailored Design
• Fatigue Life
• Dimensional Stability
• Corrosion Resistance

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Why Composites over Metals?

• How is the mechanical advantage of composite
  measured?

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Specific Strength vs. Year
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Table 1.1. Specific modulus and strength of
typical fibers,composites and bulk metals
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Specific Strength vs Specific Modulus
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Other Mechanical Parameters

• Are specific modulus and specific strength the
  only mechanical parameters used for measuring the
  relative advantage of composites over metals?
• NO!!

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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

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Fatigue Life

• Fatigue life is higher than metals such as
  aluminum.
• Important consideration in applications such as
• aircrafts
• bridges
• structures exposed to wind

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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)

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Corrosion Resistance

• Polymers and ceramics matrix are corrosion
  resistant
• Examples include
• underground storage tanks
• doors
• window frames
• structural members of offshore drilling platforms

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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!!!!

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Cost Considerations

• Composites may be more expensive per pound than
  conventional materials. Then why do we use
  composite materials?

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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

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Fiber Factors

• What fiber factors contribute to the mechanical
  performance of a composite?
• Length
• Orientation
• Shape
• Material

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Fiber Factor - Length

• Long Fibers
• Easy to orient
• Easy to process
• Higher impact resistance
• Dimensional stability
• Short Fibers
• Low Cost
• Fast cycle time

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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

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Fiber Factor - Shape

• Most common shape is circular
• Hexagon and square shapes give high packing
  factors

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Fiber Factor - Material

• Graphite and aramids have high strength and
  stiffness
• Glass has low stiffness but cost less

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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.

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Factors Other Than Fiber and Matrix

• Fiber-matrix interface
• Chemical bonding
• Mechanical bonding

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Fiber Types

• Glass Fiber (first synthetic fiber)
• Boron (first advanced fiber)
• Carbon
• Silicon Carbide

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Types of Matrices

• Polymers
• Metals
• Ceramics

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Polymer Matrix

• Thermosets
• polyester
• epoxy
• polymide
• Thermoplastics
• polypropylene
• polyvinyl chloride
• nylon

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Metal Matrix

• Aluminum
• Titanium
• Copper

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Ceramic Matrix

• Carbon
• Silicon Carbide
• Calcium AluminoSilicate
• Lithium AluminoSilicate

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Why do fibers have thin diameter?

• Less flaws
• More toughness and ductility
• Higher flexibility

Thin Fiber
Thick Fiber
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Less Flaws
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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.

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More Flexibility

• Flexibility is proportional to inverse of
• Youngs modulus
• Fourth power of diameter
• Thinner fibers hence have a higher flexibility
  and are easy to handle in manufacturing.

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Classification

• CONCRETE Gravel, sand and cement
• PAINT Paint and aluminum flakes
• GRAPHITE/EPOXYGraphite fibers in epoxy matrix

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Polymer Matrix Composites

• What are the most common advanced composites?
• Graphite/Epoxy
• Kevlar/Epoxy
• Boron/Epoxy

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Polymer Matrix Composites

• What are the drawbacks of polymer matrix
  composites?
• Low operating temperatures
• High CTE and CMEs
• Low elastic properties in certian directions

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Are Carbon and Graphite the Same?

• No
• Carbon fibers have 93-95 carbon content and
  graphite has gt99 carbon content
• Carbon fibers are produced at 2400o F and
  graphite fibers are produced at 3400o F

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Table 1.4. Typical mechanical properties of
polymer matrix composites and monolithic materials
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Comparative Stiffness of PMCs and Metals
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How to make a PMC
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Schematic of Prepreg Manufacturing
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Prepreg Boron/Epoxy
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Autoclave Lamination
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Filament Winding
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Resin Transfer Molding
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Common PMC Fibers Matrices

• Fibers
• Graphite
• Glass
• Kevlar
• Matrices
• Epoxy
• Phenolic
• Polyester

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Table 1.5 Typical mechanical properties of
fibers used in polymer matrix composites
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Cost Comparison of PMC fibers

• Type of fiber Cost ( per pound)
• A-glass .65 - .90
• C-glass .75 - 1.00
• E-glass .75 - 1.00
• S-2 Glass 6.00 - 8.00
• Heavy Tow 9.00 - 12.00
• Medium Tow 15.00 -20.00
• Low Tow 40.00 -70.00
• Kev29 12.00 -14.00
• Kev149 25.00 -30.00

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Manufacturing of Glass Fibers
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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

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Table 1.6 Comparison of properties of E-glass
and S-glass
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Table 1.7 Chemical Composition of E-Glass and
S-glass Fibers
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Fig 1.11 Manufacturing Graphite Fibers
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Resin Systems

• Polyester
• Phenolics
• Epoxy
• Silicone
• Polymide

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Properties of epoxy
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Curing Stages of Epoxy
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Comparison of Resins
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Difference between thermosets and thermoplastics
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Pre-Preg Graphite/Epoxy
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Application of Polymer Matrix Composites

• Carbon-fiber shin

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Space Shuttle
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Jet Skis
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Lear Fan
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Fighter Jets
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Corvette Leaf Springs
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Snow Skis
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I-beam
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Pressure vessels
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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.

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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.

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Degrading properties in MMCs (Fig 1.3)

• Are there any properties which degrade when
  metals are reinforced with fibers?
• Yes, they may have reduced ductility and
  fracture toughness.

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Typical mechanical properties of metal matrix
composites
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Boron Fiber
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Step 0 Cutting the shape
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Step 1 Apply Aluminum File
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Step 3 Lay Up Desired Plies
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Step 4Vacuum the specimen
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Step5 Heat to Fabrication Temperature
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Step 6 Apply Pressure and Hold for Consolidation
Cycle
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Step 7 Cool, Remove and Clean Part
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Schematic of Diffusion Bonding
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Silicon Carbide/ Aluminum Composite
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Application of MMCs
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Application of MMCs
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Application of MMCs
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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.

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Advantages of CMCs

• High strength, hardness and high service
  temperatures
• Chemical inertness
• Low Density

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Table 1.12 Typical fracture toughness of
monolithic materials and ceramic matrix composites
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Table 1.13 Typical mechanical properties of
some ceramic matrix composites
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Manufacturing of Ceramic Matrix Composites -
Slurry Infiltration
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Application of CMCs
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Carbon-Carbon Compoistes

• What are carbon-carbon composites?
• Carbon - Carbon composites have carbon fibers in
  carbon matrix.

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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

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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

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Table 1.14 Typical mechanical properties of
carbon-carbon matrix composites
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Carbon-Carbon Manufacturing (Fig 1.34)
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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

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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?

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Recycling Continued

• What are the various steps in mechanical
  recycling of short fiber-reinforced composites?
• Where are mechanically recycled short fiber
  composites used?

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Chemical Recycling

• Which chemical process shows the most promise?
• Why is chemical recycling not as popular as
  mechanical recycling?

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Definitions

• Isotropic body
• Homogeneous body
• Anisotropic body
• Nonhomogeneous body
• Lamina
• Laminate

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Schematic of Analysis of Laminated Composites
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An Artists Rendition of a Composite Material