Composite Materials

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Composite Materials

• Ahmed W. Moustafa
• Lecture (1)

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Composite Material

• Two inherently different materials that when
  combined together produce a material with
  properties that exceed the constituent materials.

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Composite Material Defined

• A materials system composed of two or more
  physically distinct phases whose combination
  produces aggregate properties that are different
  from those of its constituents

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Composite Material Defined

• Examples
• Cemented carbides (WC with Co binder)
• Plastic molding compounds containing fillers
• Rubber mixed with carbon black
• Wood (a natural composite as distinguished from a
  synthesized composite)

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Why Composites are Important

• Composites can be very strong and stiff, yet very
  light in weight, so ratios of strength-to-weight
  and stiffness-to-weight are several times greater
  than steel or aluminum
• Fatigue properties are generally better than for
  common engineering metals
• Toughness is often greater too
• Composites can be designed that do not corrode
  like steel
• Possible to achieve combinations of properties
  not attainable with metals, ceramics, or polymers
  alone

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Disadvantages and Limitations

• Properties of many important composites are
  anisotropic - the properties differ depending on
  the direction in which they are measured this
  may be an advantage or a disadvantage
• Many of the polymer-based composites are subject
  to attack by chemicals or solvents, just as the
  polymers themselves are susceptible to attack
• Composite materials are generally expensive
• Manufacturing methods for shaping composite
  materials are often slow and costly

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Classification of Composite Materials

• Traditional composites composite materials that
  occur in nature or have been produced by
  civilizations for many years
• Examples wood, concrete, asphalt
• Synthetic composites - modern material systems
  normally associated with the manufacturing
  industries, in which the components are first
  produced separately and then combined in a
  controlled way to achieve the desired structure,
  properties, and part geometry

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Components in a Composite Material

• Nearly all composite materials consist of two
  phases
• Primary phase - forms the matrix within which the
  secondary phase is imbedded
• Secondary phase - imbedded phase sometimes
  referred to as a reinforcing agent, because it
  usually serves to strengthen the composite
• The reinforcing phase may be in the form of
  fibers, particles, or various other geometries

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Functions of the Matrix Material (Primary Phase)

• Provides the bulk form of the part or product
  made of the composite material
• Holds the imbedded phase in place, usually
  enclosing and often concealing it
• When a load is applied, the matrix shares the
  load with the secondary phase, in some cases
  deforming so that the stress is essentially born
  by the reinforcing agent

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Composites Offer

• High Strength
• Light Weight
• Design Flexibility
• Consolidation of Parts
• Net Shape Manufacturing

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Fiber Reinforced Polymer Matrix

• Matrix

• Transfer Load to Reinforcement
• Temperature Resistance
• Chemical Resistance

Reinforcement

• Tensile Properties
• Stiffness
• Impact Resistance

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Design Objective

• Performance Strength, Temperature, Stiffness
• Manufacturing Techniques
• Life Cycle Considerations
• Cost

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Matrix Considerations

• End Use Temperature
• Toughness
• Cosmetic Issues
• Flame Retardant
• Processing Method
• Adhesion Requirements

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Matrix Types

• Polyester 
• Polyesters have good mechanical properties,
  electrical properties and chemical resistance.
  Polyesters are amenable to multiple fabrication
  techniques and are low cost.
•  
• Vinyl Esters
• Vinyl Esters are similar to polyester in
  performance. Vinyl esters have increased
  resistance to corrosive environments as well as a
  high degree of moisture resistance.

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Matrix Types

• Epoxy
• Epoxies have improved strength and stiffness
  properties over polyesters. Epoxies offer
  excellent corrosion resistance and resistance to
  solvents and alkalis. Cure cycles are usually
  longer than polyesters, however no by-products
  are produced.
•  
• Flexibility and improved performance is also
  achieved by the utilization of additives and
  fillers.

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Reinforcement

• Fiber Type
• Fiberglass
• Carbon
• Aramid
•  
• Textile Structure
• Unidirectional
• Woven
• Braid

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Fiberglass

• E-glass Alumina-calcium-borosilicate glass
• (electrical applications)

S-2 glass Magnesuim aluminosilicate
glass (reinforcements)
Glass offers good mechanical, electrical, and
thermal properties at a relatively low cost.
E-glass S-2 glass Density 2.56 g/cc 2.46
g/cc Tensile Strength 390 ksi 620 ksi Tensile
Modulus 10.5 msi 13 msi Elongation 4.8 5.3
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Aramid

• Kevlar Twaron
•  
• Para aramid fiber characterized by high tensile
  strength and modulus
•  
• Excellent Impact Resistance
• Good Temperature Resistance

Density 1.44 g/cc Tensile Strength 400
ksi Tensile Modulus 18 Msi Elongation 2.5
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Carbon Fiber

• PAN Fiber made from Polyacrylonitrile precursor
  fiber
•  
• High strength and stiffness
• Large variety of fiber types available

Standard Modulus Intermediate
Modulus   Density 1.79 g/cc 1.79 g/cc Tensile
Strength 600 ksi 800 ksi Tensile Modulus 33
Msi 42 Msi Elongation 1.8 1.8
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Weight Considerations

• Aramid fibers are the lightest
• 1.3-1.4 g/cc
• Carbon
• 1.79 g/c
•  
• Fiberglass is the heaviest
• 2.4 g/cc

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Strength Considerations

• Carbon is the strongest
• 600-800 ksi
• Fiberglass
• 400-600 ksi
• Aramids
• 400 ksi

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Impact Resistance

• Kevlar is the toughest
• Fiberglass
• Carbon

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Stiffness Considerations

• Carbon is the stiffest
• 30-40 msi
• Aramids
• 14 msi
• Fiberglass
• 10-13 msi

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Cost Considerations

• Fiberglass is cost effective
• 5.00-8.00/lb.
•  
• Aramids
• 20.00/lb
•  
• Carbon
• 30.00-50.00/lb

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Fabric Structures

• Woven Series of Interlaced yarns at 90 to each
  other
•  
• Knit Series of Interlooped Yarns
•  
• Braided Series of Intertwined, Spiral Yarns
•  
• Nonwoven Oriented fibers either mechanically,
  chemically, or thermally bonded

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Woven Fabrics

• Basic woven fabrics consists of two systems of
  yarns interlaced at right angles to create a
  single layer with isotropic or biaxial
  properties.

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Physical Properties

• Construction (ends picks)
• Weight
• Thickness
• Weave Type

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Components of a Woven Fabric
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Basic Weave Types
Plain Weave
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Basic Weave Types
Satin 5HS
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Basic Weave Types
2 x 2 Twill
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Basic Weave Types
Non-Crimp
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Braiding
A braid consists of two sets of yarns, which are
helically intertwined.   The resulting structure
is oriented to the longitudinal axis of the
braid.   This structure is imparted with a high
level of conformability, relative low cost and
ease of manufacture.
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Braid Structure
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Types of Braids
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Triaxial Yarns

• A system of longitudinal yarns can be introduced
  which are held in place by the braiding yarns
• These yarns will add dimensional stability,
  improve tensile properties, stiffness and
  compressive strength.
• Yarns can also be added to the core of the braid
  to form a solid braid.

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Conclusions
Composite materials offer endless design
options. Matrix, Fiber and Preform selections
are critical in the design process. Structures
can be produced with specific properties to meet
end use requirements.